Battery Tender Jr

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ebeighe

Well-known member
Joined
Jul 5, 2017
Messages
96
Location
Phoenix, AZ
I didn't buy this for my Leaf, but figured there were a lot of battery tender Jr owners here.
It seems a good price and i need something for another car i don't drive much.
u
https://slickdeals.net/f/10679860-battery-tender-junior-12v-battery-charger-6-credit-18-99

when i connected to the leaf 12v battery, the battery was already quite full as measured by a voltmeter (12.8V or something)
anyway, the BTjr it was indicating solid red ("bulk charging"; 750mAhr for the Jr.); it stayed that was even though a couple of hours later voltmeter read 13.1V
Isn't is supposed to switch modes based on voltage?
The next mode is blinking green.

I left it on the car i don't use overnight, and in the morning (so maybe 12 hours later) voltmeter was reading 14.1 and still solid red.

do i just need to wait longer?
 
Yup, your battery was likely just that low. I can't remember if the newer ones time out after 24 hours or not, but it wouldn't surprise me if it took more than 12 hours to get he battery back to full.
 
I have three of these units. I use one for my Leaf, one for a Chevy diesel truck with two large 12V batteries (in parallel), and one for motorcycles. The charge rate of 0.75 amps will get the job done eventually, but if your battery is very low, it takes a while. Also, when you charge a battery while it's installed in a vehicle, a portion of the charge current ends up powering the vehicle electronics instead of charging the battery. For example, if your leaf is drawing 0.25 amps, then there is only 0.50 amps going into the battery. That makes it take even longer. A fully discharged battery could spend days in the bulk charge phase.

The charge phases and LED states are:

Solid Red = Bulk Charge
Blinking Green = Balancing Charge (?)
Solid Green = Charge completed, float charge

But what does this actually mean? I was curious about what the charge profile looks like, so I gathered some data. What you see below is the charge profile and LED states when I charged a 51R battery outside of the vehicle after it had been discharged by a 30 amp load for 1 minute. This means approximately 1/2 amp-hour of charge would be required.

First is the bulk charge phase: In this phase, the output voltage is adjusted to keep the output current at 0.75 amps. As you can see, this phase lasts as long as necessary to bring the battery up to about 14.4 volts. Next comes the odd-looking blinking green phase. This always seems to last 15 minutes, no matter what. I'm not sure what algorithm is used to set the voltage (or current) during this phase. When that's finished, the solid green float charge phase starts. In this phase, the output remains at 13.1 volts indefinitely.

In case you are not familiar with lead acid batteries, do not worry about these voltages being much higher than 12V. This is expected, and perfectly fine for the battery and vehicle electronics.

38064300111_d1d3279368_b.jpg


So, if your battery is stuck in the solid red phase and it's below 14.4 volts, that probably just means it's slowly charging. If the voltage doesn't go up measurably in a few hours, something may be wrong.
 
Nissan Leaf's are terrible at keeping the 12v battery healthy. I plug in my battery tender to my leaf once a week during the winter and once a month during the summer, overnight. The very first time I did this.. the reading for the battery said it was ok but the tender knew better and did it's job.. red for ages and then balancing out much later than I thought. Once i started the schedule or running the tender regularly it was much faster.

I also found all the DTC error codes I had were related to the 12v battery not being able to do its job. Battery Tender took care of that.
 
I bought a 2 amp Diehard maintainer a few years ago, to get more speed. It Did NOT live up to its name, and died after about a year. Now I just use the BTJ.
 
So a blinking green + red means it's charging and also de-sulphfying?
I haven't used my Battery tender in a while and wouldn't you know, on one of the first cold days(today) my '12 Leaf failed to start! A push of the power button and all the lights came on but no ready light. I was sure it was the 12v battery so I got out my VOM and low and behold the 12v battery was only reading 9v. I hooked up my $40 12v lithium battery jumper(something I always carry in my Leaf) to the battery and it went to 12v within 30 seconds. I got in and my Leaf started like a champ. As soon as it started the 12v battery went to 14v.
Now I'm thinking the low 12v battery could have been somewhat caused by my main battery only being a SOC of ~20%?? When I got home(less than 5 minutes from where I had to jump start the Leaf) I measured the 12v battery(Leaf off) and it was 12v, as soon as I plugged the Leaf in to charge the traction battery the 12v battery went to ~13.5v, occasionally jumping to 14v. I then hooked up my Battery Tender and the red and green lights both came on, shortly after the green light started to flash(hence my first question). If I unplugged the J1772 cable the green light continued to flash, then I power cycled the Battery Tender and the flashing stopped and went solid. As soon as I plugged the J1772 cable back in the flashing started. I'm wondering if I should go out once the traction battery is charged and power cycle the Battery Tender to get it charging again? I believe once the Battery Tender starts to flash it might not start charging again unless I power cycle it, even if the 12v battery goes back low....
If this happens again I'll just replace the 12v battery, AFAIK it's the original and being a '12 could be 5+ years old. I already have a spare Optima Yellow Top I purchased last winter when I was suspecting the battery but after using my Tender every couple of weeks or so it gave me no problems last summer so I kept the original battery in the Leaf and just occasionally used my Tender on the spare Optima.
 
It sounds like you're trying to use your Battery Tender while you're also charging the car. I wouldn't recommend that, because the built-in 12v converter is also trying to output 13-14 volts at that time. If your battery tender is showing strange light patterns, it's probably a sign that it knows something odd is happening.

(BTW, you didn't mention which model you have, but the Jr only has one light and can't show both red and green at the same time)
 
It sounds like you're trying to use your Battery Tender while you're also charging the car. I wouldn't recommend that, because the built-in 12v converter is also trying to output 13-14 volts at that time.

I do this all the time, and it works fine.
 
LeftieBiker said:
It sounds like you're trying to use your Battery Tender while you're also charging the car. I wouldn't recommend that, because the built-in 12v converter is also trying to output 13-14 volts at that time.

I do this all the time, and it works fine.

Interesting. What does it do? Does the Battery Tender finish all of its phases while the car is still charging?
 
Interesting. What does it do? Does the Battery Tender finish all of its phases while the car is still charging?

Yes. Mine is hardwired to an SAE connector through the charge port compartment, but I believe it will act normally even if clipped on.
 
brotherjethro said:
It sounds like you're trying to use your Battery Tender while you're also charging the car. I wouldn't recommend that, because the built-in 12v converter is also trying to output 13-14 volts at that time. If your battery tender is showing strange light patterns, it's probably a sign that it knows something odd is happening.

(BTW, you didn't mention which model you have, but the Jr only has one light and can't show both red and green at the same time)
Yes my model of Battery Tender after charging is complete, desulphaphies?? the battery. I believe a red LED means it's hooked to the battery, a solid green LED means it's charging and a flashing LED means it's in the de-sulification mode, where it will stay until unplugged. What I don't know is once it's in the de-sulfication mode(flashing green LED) if the battery gets low will it start charging again......I know once the green LED flashes, the only way to get it to stop is to power cycle the Battery Tender, even if disconnected from the battery it will still flash, until unplugged.
 
Yes my model of Battery Tender after charging is complete, desulphaphies?? the battery. I believe a red LED means it's hooked to the battery, a solid green LED means it's charging and a flashing LED means it's in the de-sulification mode, where it will stay until unplugged.

Maybe there's a newer model that does this, but for most BTJs the solid red light means bulk charging at full power, the flashing green means it's in finish charging mode at reduced power*, and then it goes solid green when the battery is full charged, and stays there.

* Maybe the flashing green means a de-sulfating mode, because 0.75 amps isn't that much, but since these are designed for small batteries as well as larger ones, I think that this mode is to keep small motorcycle-sized batteries from charging too quickly from 90% to 100%.
 
jjeff said:
What I don't know is once it's in the de-sulfication mode(flashing green LED) if the battery gets low will it start charging again......I know once the green LED flashes, the only way to get it to stop is to power cycle the Battery Tender, even if disconnected from the battery it will still flash, until unplugged.

Yes, the BTJ monitors the battery voltage in both green modes (solid & flashing) and will switch back to bulk charge "solid red" mode and start over if needed. You can see this happen by turning on the headlights while in either green mode.
 
LeftieBiker said:
Interesting. What does it do? Does the Battery Tender finish all of its phases while the car is still charging?

Yes. Mine is hardwired to an SAE connector through the charge port compartment, but I believe it will act normally even if clipped on.

Good to know! I've been curious, but didn't want to try it.

(And mine is wired the same way, LOL).
 
LeftieBiker said:
12.8 volts isn't really "quite full." I've never had a BT JR fail, and I have several of them. Give it a bit longer.

BrockWI said:
Yup, your battery was likely just that low. I can't remember if the newer ones time out after 24 hours or not, but it wouldn't surprise me if it took more than 12 hours to get he battery back to full.

yes, as you predicted... just needed several more hours. all good.
 
jjeff said:
...de-sulphfying?
jjeff said:
...desulphaphies??
Jeff said:
...de-sulification mode,..
I love these! :D

Yes, it's a weird word. Briefly, lead sulfate forms as a white paste when a lead-acid battery discharges. When the battery is recharged, the lead sulfate is separated back into metallic lead and sulfuric acid. If the battery stays partially discharged for some amount of time (depending on temperature, etc.), some of the lead sulfate converts from the paste form into a crystal. Once the lead sulfate crystallizes, it is not as easily split back into metallic lead and sulfuric acid. In other words, it ties up both electrolyte and lead that originally was available in the charge-discharge reactions of the battery, thus reducing the capacity. Desulfating chargers typically use either higher voltages or pulses or both to try to break up the lead sulfate crystals to restore some or all of the original capacity of the battery. This typically takes more than one recharge cycle, but the battery can eventually come back close to like-new condition if such chargers are used consistently (and electrolyte levels are maintained).

So...

...desulfating.

...desulfates.

...desulfation.
 
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