Joining the 80% Club

[tbleakne]

i am actually going to "create" a 90% club. it will be my goal to determine how long i need to charge for the "long commute" days to have 90% charge.

for the short days, 80% will be more than enough since RT figures looks to be 20-30 miles if side trips are involved.

I, too would like to stop charging most of the time at 90%. I was planning to do this by careful timed charging, but I now understand that this is more difficult than it first appears because the L2 charging rate is NOTuniform. The following graph explains this:

This chart illustrates how a full Li-ion charge requires two charge phases. The first phase of the charging cycle shown is current-limited, and the second phase is voltage- limited. The Leaf's first phase is power-limited, so unlike the chart, its current will decrease as the voltage rises in this phase.

The Leaf's second phase will behave as shown, with the voltage held constant as the current decreases. The power drawn from the EVSE, current X voltage, will decrease during this phase from the nominal 3.3-3.7Kw level. Sparky has observed this effect with his Leaf, and he reports that the switch from the first to the second phase occurs at about the 80% SOC point. It is possible that this could be a major reason Nissan provided the 80% charge option, because the remaining 20% charge occurs at a slower rate that requires more time.

Credit for graph: http://www.mpoweruk.com/chargers.htm

 

[AndyH]

In other words, the bars have no strict relationship to SOC.

The 10th bar (third one down) will come on when the battery SOC crosses from 79% to 80% - but will turn off when the SOC crosses from 85% to 84%. So the meaning of the bars is relative to the direction.

I thought this was a typical way to engineer indicator lights to avoid flickering back and forth when close to between the levels.

The reason the SOC display sometimes changes when you switch to/from charging/driving is the battery's intrinsic hysteresis. Below is a graph which displays battery voltage vs SOC for both charge and discharge cycles for Li-ion chemistry.
<snip>
[/img]

Note how a given voltage has a substantially different SOC for charge and discharge. The Leaf system must compute the SOC taking this effect into account, but it can't correct perfectly, and that is why you see some changes in the display.

Credit: http://www.mpoweruk.com/chargers.htm
This site has quite a bit of valuable battery and charging info under the "Energy Storage" tab.

I'm going to say 'no' to this theory, because we know from the Leaf service manuals that the car's management system tracks each cell's voltages, current in/out, and the cell's internal resistance (the cause for the 'hysteresis' you've referenced). The car has all the info it needs to properly determine and display an accurate SOC - and does provide accurate SOC info on the CAN bus.

The battery university and mpoweruk sites do have plenty of info, unfortunately it's about 10 years out of date. Lithium is getting much of the R&D money these days and progress is happening faster than books and websites can keep up.

 

[idunk]

I am late to the party and I have skimmed most of the messages in this thread, so I don't think I am repeating, but apologies if I do. I don't own a LEAF yet, so some will be speculative.

What I plan on doing, is to try to keep the state of charge (SoC) of the battery between 20 and 80% because that's where you maximize the lifetime of the CELLS. However, every once in a while, probably every 5-10 cycles I plan on going to 100%. The reason is that cells need to be balanced to extract the maximum amount of charge from the pack.

What I will say will be slightly inaccurate, but to be accurate, I would need much more space.

The LEAF pack has 96 cells in series and the battery management system (BMS) will stop discharging when the first cell in the series hits the undervoltage limit. If the cells have a different amount of charge in them (and they will, believe me), it means that when the first cell hits the limit, the other cells will still have charge that can not be used because you gotta stop discharge. When you recharge, the charger stops the charge when the first cell hits the overvoltage limit. Hence, all other cells will not be completely full. If you keep doing this, the problem will compound unless you balance, i.e. you make sure that all cells are full at the end of the charge (or quite close to it). The problem is really dramatic, I am talking about several % of unusable capacity lost every 10,000 miles. Balancing as it is implemented in virtually all electric vehicles now basically solves the unusable capacity, but not the aging problem. Balancing is generally performed at the end of the charge cycle (don't know what the LEAF does, but I suspect that like everybody else Nissan balances at the end of the charge cycle), so you really wanna recharge to 100% (assuming that my speculation is true).

Speaking of aging, you want to keep your cells as much as possible away from "low" because the cell voltage goes down which means that the battery pack will need to supply a higher current to deliver the same power. This in turns accelerates aging because the higher the average current, the more rapid the aging. So, if you are often in the low charge area, you are increasing the average current that the battery delivers. Furthermore, when the voltage is low there is the possibility that the motor works at a lower efficiency point (I don't know whether that's the case for the LEAF though).

In Li-ion batteries, the charge is generally constant current to approximately 80% SoC (the actual number depends on the cells), in other words the charge is not really at constant power. Hence it shouldn't be linear (it will be pretty close to linear though). The last part of the charge is at constant voltage at whatever current the battery can absorb, so it will be slower as the battery will be able to absorb less and less current. Finally, when it's all done, balancing will start, which is even slower (the car will not be charging at that point, other than for brief time intervals).

As for level 1 vs. level 2 vs. level 3, I plan on charging mostly at level 2. On a 24 kWh pack, 3.3 kW implies charging at a low average current, so lifetime won't be significantly impacted (or very very little anyway). Level 3 won't impact lifetime much, but if you do it often it will be noticeable. I guess the Level 3 charge (i.e. quick charge) is just the constant current portion of the charge at a higher charge rate (known as C rate, if you read technical papers).

 

[thankyouOB]

what is the difference between 100% charge and 100% usable charge--in terms of the language not kWh?

that is to say, what are you talking about?
is their some sort of reserve to the battery that we cannot access for driving?

 

[idunk]

The difference between charge and usable charge is simple. Charge is what's inside, usable charge is what you can get out. If there is imbalance you can't use all the charge that is in the battery.
In simple terms, assume you have two cells with 220 Wh capacity, one has 200 Wh of energy inside and the other one has 220 Wh inside. If you connect them in series and discharge them, you will be able to get 400 Wh of (usable) charge, although there are 420 Wh of energy inside and the capacity is 440 Wh.

When you (passive) balance basically you burn 20 Wh in a resistor, so that the two cells contain 200 Wh each, then you start charge again and they end up (approximately) to 220 Wh, so you have 440 Wh inside and you can use all 440 Wh (in reality the charge rate, discharge rate and capacity of every cell are slightly different)

 

[AndyH]

what is the difference between 100% charge and 100% usable charge--in terms of the language not kWh?

that is to say, what are you talking about?
is their some sort of reserve to the battery that we cannot access for driving?

A plain battery - like a car battery or the D cells in a flashlight - is completely unmanaged. If we overcharge them, or leave the lights on, we can completely empty and/or destroy the batteries. Both of these allow us to use -and abuse - 100% of their capacity. We have access to the full capacity of the batteries.

The Leaf's battery has sophisticated computerized management. We do not have full access to the battery. We can only use 80% of the energy the battery can hold.

Ok...this analogy just popped in...let's try it out.

Run to the closest toilet and lift the lid off the tank. The first thing we'll notice is that the water does not come all the way to the top of the tank - the tank can hold more water but we're not using that extra capacity.

Now - flush the toilet. Once "all" the water runs out we can see that there's still water in the tank - we cannot use all the water that's stored there. Also notice as the tank fills that the water will stop again before the tank is completely filled.

We are not allowed to use 100% of the tank capacity - and we are not allowed to drain all the water from the tank.

The Leaf's battery is JUST like that. The car's management system does not let us put too much energy into the battery - we can only fill to about 95% of total (so 100% full on the fuel gauge only means the water has stopped coming in - it doesn't mean the tank is going to overflow. ) At the end of a 100 mile drive, as the last red bar goes dark and the remaining range display changes to --- and the turtle light comes on, we know that we've used all the energy that the Nissan engineers have set aside for us. But just like the toilet tank there is still energy in the battery. We cannot use it, but that energy remaining - that last 15% - is helping our battery last.

100% "consumer" - a full tank on the fuel gauge - is only about 95% of what the battery can hold.
0% "consumer" - an empty tank and a turtle light - leaves about 15% in the battery.
100% consumer capacity is only using about 80% of the energy the battery can hold.

No - there's no reserve. In order to get a long life from the battery we only want to use about 80% of the total capacity. The 5% we cannot access on top, and the 15% we cannot use on the bottom is helping us get an 8-10 year battery life.

(please let me know if that makes sense. I may have to flush another analogy. )

 

[AndyH]

Ignore imbalance, idunk. You and others are thinking of the battery from the viewpoint of a Nissan engineer or a DIYer that's just installed a 'naked' and unmanaged battery.

We're not engineering the battery - we're only talking about what we can access as consumers.

Your imbalance talk is off the mark anyway as the car has a sophisticated management system that balances, tracks and adjusts for capacity and internal resistance changes, and yes - as a last resort - shuts things down if a cell pair hits over- or under-voltage.

We don't have to restrict charging to only use 80% because the car does that.
We don't have to charge to 100% from time to time to balance the cells because the car can adjust in mid-cycle if it wants.
We don't have to limit our 'fuel' use to only the white bars, or to only use one red bar because the 'fuel gauge' shows us what we can use - and we can use it all if we want. We do not have to worry about damaging cells because...

(You guessed it) The Car Does That.

 

[DrPowell]

So the quoted 24 kWh capacity of LEAF's pack is the accessible capacity (80%), and its raw capacity is ~30?

 

[idunk]

Ignore imbalance, idunk. You and others are thinking of the battery from the viewpoint of a Nissan engineer or a DIYer that's just installed a 'naked' and unmanaged battery.

We're not engineering the battery - we're only talking about what we can access as consumers.

Your imbalance talk is off the mark anyway as the car has a sophisticated management system that balances, tracks and adjusts for capacity and internal resistance changes, and yes - as a last resort - shuts things down if a cell pair hits over- or under-voltage.

We don't have to restrict charging to only use 80% because the car does that.
We don't have to charge to 100% from time to time to balance the cells because the car can adjust in mid-cycle if it wants.
We don't have to limit our 'fuel' use to only the white bars, or to only use one red bar because the 'fuel gauge' shows us what we can use - and we can use it all if we want. We do not have to worry about damaging cells because...

(You guessed it) The Car Does That.

While I have no specific knowledge of what the LEAF does, other than what's in the news, I work exactly on battery management systems. That's how I make my living and I actually sell to car makers and their suppliers, so I have quite an intimate knowledge of what the big guys in the car industry do. Of course, I do not assume to know everything (actually quite the contrary), but I surely know more than the average LEAF owner.

Based on the publicly available information and the semi-public available information (i.e. industry conferences and hallway chats), it looks like the LEAF uses 100% of the DoD range (depth of discharge), that's why I plan on not using the whole DoD range, but only the 20-80% zone as much as I can. The Volt only uses 10.4 of the 14 kWh and does exactly what you say, so no need to worry if you have a Volt.

As for balancing in the middle of the charge cycle, yes, it's possible, but it's not the norm in the industry right now. I don't know whether the LEAF does it or not, so I can only tell you what I see in general.

 

[AndyH]

So the quoted 24 kWh capacity of LEAF's pack is the accessible capacity (80%), and its raw capacity is ~30?

Yes. We think the full capacity is 27-28kWh but that's not fully nailed down.

Nissan has stated that the energy available for us to use is 24kWh while the total pack capacity is proprietary.

 

[AndyH]

Ignore imbalance, idunk. You and others are thinking of the battery from the viewpoint of a Nissan engineer or a DIYer that's just installed a 'naked' and unmanaged battery.

We're not engineering the battery - we're only talking about what we can access as consumers.

Your imbalance talk is off the mark anyway as the car has a sophisticated management system that balances, tracks and adjusts for capacity and internal resistance changes, and yes - as a last resort - shuts things down if a cell pair hits over- or under-voltage.

We don't have to restrict charging to only use 80% because the car does that.
We don't have to charge to 100% from time to time to balance the cells because the car can adjust in mid-cycle if it wants.
We don't have to limit our 'fuel' use to only the white bars, or to only use one red bar because the 'fuel gauge' shows us what we can use - and we can use it all if we want. We do not have to worry about damaging cells because...

(You guessed it) The Car Does That.

While I have no specific knowledge of what the LEAF does, other than what's in the news, I work exactly on battery management systems. That's how I make my living and I actually sell to car makers and their suppliers, so I have quite an intimate knowledge of what the big guys in the car industry do. Of course, I do not assume to know everything (actually quite the contrary), but I surely know more than the average LEAF owner.

Based on the publicly available information and the semi-public available information (i.e. industry conferences and hallway chats), it looks like the LEAF uses 100% of the DoD range (depth of discharge), that's why I plan on not using the DoD range, but only the 20-80% zone as much as I can. The Volt only uses 10.4 of the 14 kWh and does exactly what you say, so no need to worry if you have a Volt.

As for balancing in the middle of the charge cycle, yes, it's possible, but it's not the norm in the industry right now. I don't know whether the LEAF does it or not, so I can only tell you what I see in general.

Welcome. I, too, work with lithium (LiFePO4, LiFeMnPO4, LICo/LiPo, and LiMN2O4), build BMSs and sell parts and packs - it's good to know we're looking at the problem from a similar perspective.

Based on knowledge of lithium in general and LiMn2O4 in particular, industry papers, and the management numbers Nissan publishes in their service manuals, it's very clear that that the Leaf actually does NOT allow us to use 100% of the battery's capacity. It would be stupid of a manufacturer - especially one providing a warranty - to give a consumer access to 100% of ultimate capacity, right?

The car's management system will only give us access to approximately 80% of total pack capacity. It appears to be 80 to 84%.

Absolutely - you're certainly welcome to use only 80% of the 80% given to us - and it might give a bit longer pack life. Any small gains may be lost in the noise of chronological degradation though. Since LiMN2O4, like LiCo/LiPo carries more of its energy at a higher voltage, and is appears that our consumer range is from 15% to 95% ultimate, your best bang for the buck would be to set the charge timer to 80%. Even if you drive until the car stops, you're still leaving about 15% in the battery. But you don't have to reinvent the wheel Nissan's already provided for our use.

We've got a number of engineers on the forum - including a number with specific battery construction, management, and integration experience. We've also got plenty of EVers here - from 1990s era and current production vehicles to conversions. But more importantly - we've got a LOT of people with zero EV experience - and all this engineering-side talk or just plain bad information based on guesses or ego is pushing people away or making them feel less secure about their decision rather than helping.

 

[idunk]

We've got a number of engineers on the forum - including a number with specific battery construction, management, and integration experience. We've also got plenty of EVers here - from 1990s era and current production vehicles to conversions. But more importantly - we've got a LOT of people with zero EV experience - and all this engineering-side talk or just plain bad information based on guesses or ego is pushing people away or making them feel less secure about their decision rather than helping.

Then let's prevent a shouting match and take this conversation private. When we agree on something (if ever) we can post our conclusion

 

[GaslessInSeattle]

I've read through this whole thread and I see some folks stating some things as facts and others refuting them with an equal tone of certainty. I've been involved in technical diving forums so I'm somewhat used to having to sort through it on my own and I assume that even the best minds will differ and even evolve their thinking over time, sometimes coming to the opposite conclusion.

Questions for any of you battery Gurus (folks who actually work with this type of battery in other applications or have some level of authority on the subject):

1. Are any of you certain the leaf only allows access to 80% of it's capacity and if so do you have a sense of how much a difference charging to 80% vs 100% of the allowed 80% capacity will make over, say 10 years?

2. If no one is certain that 100% of allowed capacity is 80% of actual, how much capacity are we likely to loose over, say 10 years if we charge to 100% as much as possible.

2. Is it valuable to run the battery all the way down every once in a while and then recharge to 100% (or in actual terms down to aprox 15 and up to 80-84% raw capacity)?

3. The best battery longevity I've gotten out of cell phones, shavers and lap tops is to charge them frequently, leaving them plugged in nearly all the time, relying on the upper end of the charge capacity and very infrequently draining them all the way down (once a month or so) and immediately charging them back up and leaving them charging for prolonged periods (not sure if there is any true trickle charging going on with the leaf charging system options after max charge is reached). Is it worth using this with my Leaf?

4. Is using the L1 charger that comes with the car better than L2, enough to favor it's use whenever possible? I've read that the L2 charger is more sophisticated and better and Nissan recommends using L1 sparingly... not sure what that is based on, maybe just that charging frequently should be done with a hard wired connection rather than a standard plug to reduce chance of corrosion resistance/fire risk.

5. it's tempting to not want to baby the batteries too much and have them die shortly after the warranty runs out vs before... then again, I'm guessing the warranty will only cover failed cells and not a total cluster replacement.

It's understandable that we all are a little leery, given the roomers such as the batteries could account for $18K of the car, with no current replacement cost known, should one somehow violate warranty and get stuck with the bill after killing the cluster, it could be devastating. (I had VW play some interesting games with me on a Diesel Jetta I owned, claiming warranty violations that were essentially impossible to disprove) I heard Nissan has $500,000,000 sunk into R&D; it feels a little bit like we early adapters are driving around a million dollar vehicle, gulp!

I'm repeating some questions I previously posted so sorry for the re-posting.

Kind Regards,
George

 

[idunk]

AndyH and I are still disagreeing, but I still like him

 

[LEAFfan]

3. The best battery longevity I've gotten out of cell phones, shavers and lap tops is to charge them frequently, leaving them plugged in nearly all the time, relying on the upper end of the charge capacity and very infrequently draining them all the way down (once a month or so) and immediately charging them back up and leaving them charging for prolonged periods (not sure if there is any true trickle charging going on with the leaf charging system options after max charge is reached). Is it worth using this with my Leaf?

What you are describing is true for Nicads, but not lithium batteries. I used to do the same thing with nicads and had them last a long time, even ten years with a Panasonic phone without ever draining them once.
The manufacturer recommends you remove the charger on lithium cell phone batteries as soon as it is done charging.

 

[GaslessInSeattle]

3. The best battery longevity I've gotten out of cell phones, shavers and lap tops is to charge them frequently, leaving them plugged in nearly all the time, relying on the upper end of the charge capacity and very infrequently draining them all the way down (once a month or so) and immediately charging them back up and leaving them charging for prolonged periods (not sure if there is any true trickle charging going on with the leaf charging system options after max charge is reached). Is it worth using this with my Leaf?

What you are describing is true for Nicads, but not lithium batteries. I used to do the same thing with nicads and had them last a long time, even ten years with a Panasonic phone without ever draining them once.
The manufacturer recommends you remove the charger on lithium cell phone batteries as soon as it is done charging.

What I'm describing is my experience with NMH and Lithium ion. I gave up on Nicads a long time ago. I guess my experience with my iphone is a bit different and it has really held up well over the last 3.5 years, the longest of any cell phone I've owned. I've never put so many cycles on any battery and had it still have good capacity... apparently not all batteries are created equal or maybe I just got lucky. I use it quite a bit every day, charge it to full capacity each night. I just don't know if my experience with my iphone is in any way comparable to the beast of a battery system in my Leaf but my use pattern may match up better than say with my lap top, which I tend to use like a desk top, plugged in mostly.

Maybe i'm talking myself into the choice of fully charging to 100% each night, accepting that the battery will degrade some (10%-15% over 10 years) no matter what but that it will hold up pretty well while giving me maximum range for convenience. agree/disagree?

G

 

[Volusiano]

3. The best battery longevity I've gotten out of cell phones, shavers and lap tops is to charge them frequently, leaving them plugged in nearly all the time, relying on the upper end of the charge capacity and very infrequently draining them all the way down (once a month or so) and immediately charging them back up and leaving them charging for prolonged periods (not sure if there is any true trickle charging going on with the leaf charging system options after max charge is reached). Is it worth using this with my Leaf?

What you are describing is true for Nicads, but not lithium batteries. I used to do the same thing with nicads and had them last a long time, even ten years with a Panasonic phone without ever draining them once.
The manufacturer recommends you remove the charger on lithium cell phone batteries as soon as it is done charging.

Whoever said NiCad works best by being topped off all the times no matter what their charge level is at is wrong. NiCads don't like to be topped off before they get discharged first because otherwise they'd have a memory problem (the ability to fully recharge to 100% is diminished). That's why NiCads need to be reconditioned frequently (get a deep discharge on purpose, even if there's still some juice left) before they should receive a full charge again.

NiMH don't have as a severe memory problem as NiCad, but it still does have a mild memory problem, and therefore occasionally can still benefit from a deep discharge/full recharge cycle (reconditioning).

The biggest problem that plague NiCad and NiMH is that if they don't get used frequently every day, they lose their charge gradually over time, and within a month or so they can be so self-discharged that they'd be rendered unusable.

They work best if you exercise them everyday and use up most of their capacity by the end of the day before recharging. From this perspective, it may look like they like to be topped off all the times. But in reality, they only like to be topped off after they've had a heavy discharge.

What I'm describing is my experience with NMH and Lithium ion. I gave up on Nicads a long time ago. I guess my experience with my iphone is a bit different and it has really held up well over the last 3.5 years, the longest of any cell phone I've owned. I've never put so many cycles on any battery and had it still have good capacity... apparently not all batteries are created equal or maybe I just got lucky. I use it quite a bit every day, charge it to full capacity each night. I just don't know if my experience with my iphone is in any way comparable to the beast of a battery system in my Leaf but my use pattern may match up better than say with my lap top, which I tend to use like a desk top, plugged in mostly.

Maybe i'm talking myself into the choice of fully charging to 100% each night, accepting that the battery will degrade some (10%-15% over 10 years) no matter what but that it will hold up pretty well while giving me maximum range for convenience. agree/disagree?

G

True that Lithium Ion batteries in cell phones and laptops like to be topped off. But they're of the Lithium Colbalt Oxide chemistry while the Leaf has the Lithium Manganese Oxide chemistry. So it's not exactly apple to apple comparison either.

I agree that while it's good to keep the Leaf battery topped off, if Nissan made it clear that topping it off to 80% is better than 100%, why would you want to top it off to 100% every night if you don't need to?

You're just assuming that your iPhone is topped off to its real 100% capacity every night, but this can easily be a wrong assumption. Apple could have easily built their charger to only top off at 80% of the real capacity every night and not tell you, therefore leading you to believe that you're topping off to 100% real capacity while maybe you're only topping off to 80% and never truly have a choice given by Apple to top it off to the real 100%.

You only know about the 80% vs 100% because Nissan chooses to tell you about it, and give you an option to charge at either level. If Nissan hasn't told you about it and decided to allow you to charge up to 80% only, and let you believe that it's 100%, you'd never know anyway.

The reason Nissan came clean about the 80% vs 100% and gave you a choice between these 2 is because they need to advertise the longest range possible for marketing purposes. After all, it's better to advertise the Leaf can go 100 miles than to advertise that it should only go up to 80 miles most of the times for longevity reason.

 

[AndyH]

AndyH and I are still disagreeing, but I still like him

Roj - agreed!

Life it good! :lol:

 

[LEAFfan]

Whoever said NiCad works best by being topped off all the times no matter what their charge level is at is wrong. NiCads don't like to be topped off before they get discharged first because otherwise they'd have a memory problem (the ability to fully recharge to 100% is diminished). That's why NiCads need to be reconditioned frequently (get a deep discharge on purpose, even if there's still some juice left) before they should receive a full charge again.

Well, it's obvious to me that you haven't used NiCads much. I'm speaking from experience, not theory. How many people have had their NiCads last ten years in a remote phone? You know why they haven't? Because they allow them to discharge completely, then put it back in the cradle to recharge. They'll be lucky to get 2-3 years. I, on the other hand, used the phone for 1-30 mins. or so, then put it back in the cradle for recharging. The pack worked great for ten years! I've done that with other NiCads also and kept them on charge for a long time, such as my radio-controlled heli transmitter which I kept on charge for over 7 years (when I wasn't using it) and they still kept a full charge when I chose to use it. I could go on and on about all the NiCads that I've done the same thing with and they've lasted a long, long , time.

 

[Volusiano]

Whoever said NiCad works best by being topped off all the times no matter what their charge level is at is wrong. NiCads don't like to be topped off before they get discharged first because otherwise they'd have a memory problem (the ability to fully recharge to 100% is diminished). That's why NiCads need to be reconditioned frequently (get a deep discharge on purpose, even if there's still some juice left) before they should receive a full charge again.

Well, it's obvious to me that you haven't used NiCads much. I'm speaking from experience, not theory. How many people have had their NiCads last ten years in a remote phone? You know why they haven't? Because they allow them to discharge completely, then put it back in the cradle to recharge. They'll be lucky to get 2-3 years. I, on the other hand, used the phone for 1-30 mins. or so, then put it back in the cradle for recharging. The pack worked great for ten years! I've done that with other NiCads also and kept them on charge for a long time, such as my radio-controlled heli transmitter which I kept on charge for over 7 years (when I wasn't using it) and they still kept a full charge when I chose to use it. I could go on and on about all the NiCads that I've done the same thing with and they've lasted a long, long , time.

Contrary to your guess, I've used lots of NiCads in the old days as well. I have some wireless land-line based phone and have experienced great longevity with NiCads like you have, so I know what you're talking about. However, I've also used them on other wireless land-line based phone where the NiCads in them don't last as long at all. It boils down to whether those phones chargers are smart chargers or not. If they're smart chargers that can automatically recondition the batteries for you, then of course the batteries will last longer. But on the wireless phone I have that doesn't have a smart charger and truly tops off when I replace it in the holder without reconditioning, those NiCads didn't last long at all for me.

And I've also used lots of NiCads back then for a variety of devices (toys, flashlights, RC cars, camcorder batteries, etc) where they didn't last long, suffered from memory effect, and worst of all, self discharged in between uses before I get to use them again the next time.

I suspect the reason your heli transmitter's NiCads last a long time is because you kept them constantly on charge and the charger must have had an automatic trickle charge mode. This way of keeping them constantly on charge is not the same as topping off I'm talking about. The topping off that I'm talking about is to partially use the batteries (let's say to 70%), then recharging them back to 100% from the partial use state. If you keep doing this many times, after receiving only 30% capacity charges each time for a while, the NiCad develops a memory effect for 30% capacity charge only, so when you deplete it down to let's say 35% next time, it'll only charge up to about 65% and stop there, instead of charging to 100%.

The memory effect on NiCad is VERY WELL KNOWN. I didn't make it up. You can Google up hundreds of hits on it easily. There used to be tons of NiCad chargers that has built-in reconditioner to discharge them fully before a recharge to erase the memory.

You've had success with your NiCads probably because you either have a smart chargers that automatically recondition the battery for you without your knowing it, or because your use model of keeping them constantly on charge 24/7 on a smart trickle charger ensure that you don't have many partially charge/recharge cycle. What most other people do (because they don't keep their NiCad on a constanty charge trickle/smart charger) is they let the batteries sit by themselves, the batteries get partially self discharged, and when they need them, they top them off from a partially charge state, thereby making the memory effect worse and worse. This is the topping off I'm talking about.