Battery heater drain in COLD weather question

How long will the battery heater keep my Li-ion battery warm if I leave my 2012 Leaf SL unplugged, assuming the outside temp is minus 10 Fahrenheit (-23 C)?

I commute to work and park my car in a parking garage at the start of the day with about 7 bars of charge left on the available charge gauge (the guess-o-meter). I have always plugged the car in when it's below -4 F, as the owner's manual recommends, but I'm wondering if that's really necessary. Will I still have a working car when I come out to start it at the end of an 8 hour day?

How many bars will I lose on the available charge gauge if the battery heater is operating for 8 hours? By my calculations, the loss would be about 1 bar. The battery heater uses 300 watts. 300 X 8 hours = 2400 watts, or 2.4 kWh. On a 24 kWh battery, that translates to a 10 percent loss. Can anyone tell me if this is how the Leaf operates in the real world?

It's unlikely that the heater would start right after you shut the car off. You might have it come on near the end of the day, but unless you have a really short commute that fails to warm the pack with power draw, I'd *guess* maybe three hours of drain from it, at most, probably less.

LeftieBiker said:

It's unlikely that the heater would start right after you shut the car off. You might have it come on near the end of the day, but unless you have a really short commute that fails to warm the pack with power draw, I'd *guess* maybe three hours of drain from it, at most, probably less.

Click to expand...

Indeed.
The battery heater only operates to keep the packs above freezing. The 300W is probably also it's peak rating, not it's continuous rating. 300W of heat is… a lot. About 1000 BTU per hour, or, enough to hold 72° for about 10x10 area.

If 10% is your cutoff, you're actually losing more range from the temperature than the heater, as simply being at 30° instead of 60° can cut off as much as 20%, and the heater hasn't even kicked in yet.

How long can it last? It's hard to say. There is a lot that comes into play on calculating this. Airflow, ambient temp, and battery temp are the 3 biggest factors. At the very least, I'd expect 3-4 days before you saw a significant (>10%) loss directly attributable to the heater. Parking outside in a windy area with the -10° weather, you might last 2 days before it's totally dead. In either case, you're probably fine for day parking at work.

mctom987 said:

...How long can it last? It's hard to say. There is a lot that comes into play on calculating this. Airflow, ambient temp, and battery temp are the 3 biggest factors. At the very least, I'd expect 3-4 days before you saw a significant (>10%) loss directly attributable to the heater. Parking outside in a windy area with the -10° weather, you might last 2 days before it's totally dead. In either case, you're probably fine for day parking at work.

Click to expand...

FWIW, the battery heater no longer operates below 30% SOC when the car is unplugged. From the manual:

The Li-ion battery warmer does not operate if the available Li-ion battery charge is less than approximately 30% and the charger is not connected to the vehicle.

Click to expand...

Some people say that the Li-ion battery should not be left at full charge for a significant amount of time. If this is true isn't it a problem leaving the car plugged in the winter time here in the North to keep the battery warm? I doubt that the first sentence is correct. My 2014 S leaf will not automatically shut off until the battery is fully charged, at any time. Neither the don't store full nor the 80% charge limit shows up in the manual. Are these just urban myths?

boba said:

Some people say that the Li-ion battery should not be left at full charge for a significant amount of time. If this is true isn't it a problem leaving the car plugged in the winter time here in the North to keep the battery warm? I doubt that the first sentence is correct. My 2014 S leaf will not automatically shut off until the battery is fully charged, at any time. Neither the don't store full nor the 80% charge limit shows up in the manual. Are these just urban myths?

Click to expand...

No, they are history rather than myth. The Leaf used to be able to stop at 80% automatically, first using the charge timer and then, in 2013 only, using an option in the car's settings as well. The EPA responded to the latter with a reduced range estimate based on averaging the two settings, and Nissan promptly dropped it for later years.

That's a relief. Thank you for the info.

LeftieBiker said:

... The EPA responded to the latter with a reduced range estimate based on averaging the two settings, and Nissan promptly dropped it for later years.

Click to expand...

A decision driven by marketing.
Nissan considered the increased sales from the misleading higher range number worth more than the costs from doing more capacity warranty battery replacements.

It doesn't mean that having the battery at lower state of charge isn't better for battery life. How much is very debateable. Not much good data to quantify it. Hard to find enough cases with identical treatment some with 100% charging, some with 80%.

So we and maybe even Nissan don't know the real impact of one versus the other.

This seems as good a place as any to point out that the temp. range of battery heating is apparently adjusted slightly on the 2015 (which has the new "lizard" battery chemistry). Owners manual says battery heater kicks on at a battery temp of -1F(-17C) and turns off when battery temp reaches 14F(-10C).

So a 2015 will only attempt to heat the battery 7C degrees. IIRC older models heat 10C degrees before shutting off. Still says the heater is only used when SOC is over 30%.

And yes, as pointed out above, this tends to say that when it's cold, you should leave it plugged in and thus conflicts with the recc. to NOT sit at 100% SOC for long periods of time. Can only suggest using Carwings and charge timer to avoid the 100% charge. The battery heater draws power from the plug if available, even when charging is not currently active.

You can also use the climate control timer to use up some charge and keep it charging longer, but unless it's near when you leave (which would obviate the need to do it) it's kind of wasteful. This is where L-1 charging is really handy.

kikngas said:

This seems as good a place as any to point out that the temp. range of battery heating is apparently adjusted slightly on the 2015 (which has the new "lizard" battery chemistry). Owners manual says battery heater kicks on at a battery temp of -1F(-17C) and turns off when battery temp reaches 14F(-10C).

So a 2015 will only attempt to heat the battery 7C degrees. IIRC older models heat 10C degrees before shutting off. Still says the heater is only used when SOC is over 30%.

Click to expand...

Interesting. My guess is that the change in start temp for the battery heater is intended to keep it charging and working better than letting it get down to -20ºC.

And yes, as pointed out above, this tends to say that when it's cold, you should leave it plugged in and thus conflicts with the recc. to NOT sit at 100% SOC for long periods of time. Can only suggest using Carwings and charge timer to avoid the 100% charge. The battery heater draws power from the plug if available, even when charging is not currently active.

Click to expand...

Plugged-in doesn't have to mean charging. That's what the charging timer is for, as you suggest. But that is a lot harder to do with the S model and its single end-time-only timer, with no days of the week settings.

However, leaving the car at "100%" (actually ~93-96%) with a battery temperature around -10ºC isn't likely to be deleterious to the battery. And charging tends to be slower at low battery temperatures.

Actually, my 2015 S does have days of week on the charge timer.

kikngas said:

Actually, my 2015 S does have days of week on the charge timer.

Click to expand...

Nice to hear. That's a considerable improvement over the earlier version.

Edit: Looking at the 2015 LEAF manual I can't find anything about days of the week for the S model, just the usual single end-time-only timer. How does it work?

Using that, one could set a charge time for later in the week and leave the car plugged-in for days during a very cold weather pattern.

It sure sounds as if the 2015 S is a big improvement over the more basic 2013 and 2014 versions. For me, the big one would be cruise control; I use it a lot and wouldn't like to be without it.

dgpcolorado said:

kikngas said:

Actually, my 2015 S does have days of week on the charge timer.

Click to expand...

Nice to hear. That's a considerable improvement over the earlier version.

Edit: Looking at the 2015 LEAF manual I can't find anything about days of the week for the S model, just the usual single end-time-only timer. How does it work?

Click to expand...

My apologies. I was recalling the climate control timer with days of week settings. You are correct, in a 2015 LEAF "without navigation system" (i.e. a model S) the charge timer is only set with an end time of day.

Since the manual warns:

The 12-volt battery can become discharged if the charging timer is operated repeatedly between the Li-ion battery charges while the vehicle is not used for an extended period of time.

Click to expand...

This warning does not appear on the "without navigation system" side. I've read elsewhere that the 12v is drained by the electronics running the charging (that reports events etc.) and so this is a way in which being plugged in works against you. If you were not plugged in, those electronics would not be active and the 12v becoming drained is much less of an issue. I believe that once the S charges based on the end timer, it essentially deactivates the charging. So it won't try to kick in every 24hrs and charge again on that end time. ...and therefore I presume the S does not actually have the 12v discharge problem, hence not stating the warning there.

I liked the suggestion given in an article that if you must leave your LEAF during extreme cold, perhaps it would be best to leave it with a friend or relative that might enjoy the EV driving experience while you are gone. Being used and charged/discharged is actually better in a number of ways than letting it sit in the cold.