Unfortunately I will have keep my Clarity outside for almost a month in the cold Quebec winter (dipping to -30 potentially). For my ICE cars, I have always removed the 12v battery in this situation and have stored it in warm storage as It would kill it if I left it. Does anyone know if the big battery would charge the 12v battery even if the car is turned off? I plan to leave the big battery charged to about 60% and not plugged in (not to be at 100% for prolonged period). thanks
I'm not sure that your customary warm storage was useful or necessary. 12V batteries don't perform at their best when severely cold but they also don't self discharge as rapidly as in milder temperatures. In your situation I might be tempted to disconnect the battery (just the negative cable is easiest) and leave it in the car. This avoids any parasitic discharge due to the keyless entry and such.
According to all posts on this forum and my own VOM testing, the 17 kWh traction battery will not charge the 12 V battery when the Clarity is off. I have no experience as to the best practice for one month at -30 C (22 below for us Metrically challenged), since I refuse to move any further north than Kentucky. I’d suggest a battery minder (trickle charger) if you can get an extension cord to it or even @css28 ’s idea of disconnecting the battery. Both are easier than taking it inside, but as you’ve found out, just leaving it alone is not an option in this case. You can expect a lot of warning indicators after reconnecting the battery, but they are harmless and will go away after a short drive. You may have to reset the TPMS, but that’s just an easy-peasy menu choice. The good news is that you won’t loose settings like radio presets and anything set by menu choices. Best wishes, but I’m shivering just thinking about your temps.
Few of us have experience with leaving a car outside unused for a month in those temps. As such, I recommend you do the same thing you have done with your ICE cars, since that worked for you in the past. As noted above, the HV battery will not charge the 12V battery when off and I like your plan to leave the HV battery at a percent charge and not plugged in. Make sure you protect your car from rodents while stored.
I will see if I can run a cable to charge it in a way not to interfere with the operation of my snow plowing guy. Otherwise I will bring it inside quick search: https://www.roadandtrack.com/car-culture/a22871/how-to-keep-your-car-battery-alive-through-a-long-cold-winter/ Car batteries aren't as trouble-free as some other parts of your car. They work best in warm climates, and need to be constantly fed with energy to keep those internal chemical reactions balanced—even when the car it's attached to isn't being driven often. Store a car battery long enough, and it's guaranteed to discharge, no matter the temperature (we're looking at you, Californians with garage queens). In particularly bad scenarios, a depleted battery's electrolyte gets to freezing temps, and crack the internals (and sometimes the case itself). Store your batteries properly, though, and these problems won't happen.
Oh, and I forgot to mention- I bought a showroom model from the dealer, and they had to boost the battery the first time I went to see it. It was completely dead. A month later when I took possession, they had to replace with a new battery as they simply charged the original one before the delivery. Obviously it didn’t hold much. My point is, once battery is completely depleted, it needs to be replaced as it’s paperweight.
