Battery in Cold Temperature

The system will protect the battery by refusing to start if the battery is too cold, so I don't think you will hurt it by letting it sit unplugged. However your Canadian model's battery warmer won't work if you are not plugged in. The manual indicates that -30C battery temperature is the point where the car won't start, but even if it doesn't get that cold the manual suggests keeping it plugged in so that the using the battery warmer can maintain the temperature for better efficiency.

Whether you should wait to plug in and run the battery warmer the night before you use the car, I don't know. I'm not sure that the battery warmer has enough power to raise the temperature or to just maintain it. I think that's why the manual recommends keeping it plugged in so that the battery warmer can maintain the temperature and keep it from getting cold and less efficient, or worse case cold enough that the car won't start. The manual indicates that the battery warmer will not operate if it gets that cold, so then you would be somewhat stuck.

 

It depends on whether your car has a battery heater. This should be mandatory in areas with cold winters as I have been led to believe that those temperatures will "brick" your battery if it doesn't have one. I have a 2018 40kwh Leaf which spent almost a week unplugged outside after I had to self isolate for 5 days due to covid exposure. Like other nights I've deliberately left it unplugged to see what would happen the temperature has never showed less than 3 bars our of 12. The drain seems to be very minimal. I don't know how they do it.

There has been much bally hoo about the Leaf not having active battery temperature management but cold batteries are only one factor in cold weather range loss, the others being denser cold air and higher rolling resistance winter tires. Getting back to your car if you can call up a battery temperature display just look at it in the morning before starting off. If you're brave leave the car unplugged on a cold night and see where it is in the morning. You could check with the dealer to see whether they can verify the presence of a battery heater but I wouldn't count on them to know. Do let us know how it works out.

 

I won't profess to be an expert on this but if your battery is bricked it won't accept a charge until it warms up so there could be a delay until it's warmed enough to charge. I have no idea whether or not the cells can actually be damaged by being subjected to these temperatures. Perhaps some others will chime in on that.

 

Only Canadian models have the battery warmer. Presumably that was an American Honda Motor Company decision not a Honda Motor Company decision. Honda Canada is a different sales organization and that's why there are a few differences, like no power seats in Canada not even in the Touring model

 

I have read that lithium batteries won't be damaged by cold temperature, they are only damaged if they are operated in temperatures below a certain point. But the system prevents that, if it gets too cold it won't let you start the car or charge it or even use the battery warmer. The owners manual doesn't warn against leaving the car out in the cold in terms of harming the battery, it only mentions lower efficiency, or the possibility that the car won't start. Honda is on the hook for 8-10 years of battery warranty so presumably they would say something if it would harm the battery to let the car sit several days unplugged in sub-freezing weather.

 

If your battery SOC drops below a certain amount (it's 30% with the Leaf) the battery warmer is turned off. So here's what I would do. Make a note of your SOC when the car is to be left for a few days. Check it each morning to make a note of any decline. This will give you a handle on how much charge you can expect to lose every 24 hours due to the battery warmer. You'll know whether or not you need to top up to keep it above 30% before the end of the idle period.

You could also use your car's built in charge timer to say give it 1/2 hour every 24 hours and just leave it plugged in. That way the battery warmer will operate off grid power instead of the battery. Then you can charge to whatever level you normally do the night before your next day's use.

 

You seem to be under the impression that the Clarity battery warmer can be powered by the HV battery, like it apparently can be in your Leaf. It can't. According to the owners manual the Clarity battery warmer only works when the car is plugged in. The SOC of the HV battery has no impact on whether the battery warmer runs or not, since the warmer is always powered by the grid.

The Clarity battery warmer runs based on battery temperature regardless of whether the car is charging or not. Although the owners manual does state that charging may take longer if the battery warmer is operating while charging.

 

My understanding is that the battery can be safely discharged at temps well below freezing but charging at temps below freezing is harmful. I suspect the degree of damage increases with the extent below freezing.

 

You won't have a problem with your traction battery if you leave it with some measure of SOC. I leave my Claire with 70-80 SOC for months of inactivity in Michigan's winter. I also have the 12V battery on a battery tender for those months . It's worked for the last 3 winters with very little 12V or traction battery degradation. If you are going to try and start your Canadian model with temps below a certain temp (tells you in your manual) you'll want to have it plugged in prior to starting the car. I never leave my car at 100 SOC for more than a day or so especially in colder temps.

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