PianoAl wrote: ↑
Thu Aug 22, 2019 8:38 am
Today I had the emergency flashers on for two hours on my 2016 Leaf. That apparently drained the 12V battery, since I couldn't open the car with the button. I got in with the physical key and used jumper cables to get things up and running.
Here are my questions:
1. Does this indicate that I should get a new 12V battery?
Hard to say. The battery should be able to blink the lamps for 2 hours no problem, but the LEAF has the added complexity that the flashers are controlled by the brake control module, which is also consuming power, keeping the emergency braking capacitor bank charged, etc... I don't know what the actual consumption is, but I'd probably try to leave the car in READY mode if needing to flashers for an extended period (more than 30 min), to keep the 12V charging.
That being said, a conventional auto battery will suffer if it's run down to very low voltage. I'd say a load test is in order to determine its health. Places like Autozone can do this for you free of charge. Ideally get a load tester or battery analyzer to check the health periodically. You can then be proactive with replacement without guessing and wasting money by replacing on a hunch. ICE cars have built-in battery testers (starter becomes sluggish with weak battery) LEAF doesn't complain until battery drops below a threshold and then all manner of errors and weird behaviors can arise.
2. If this happens again, can I assume that I can just disconnect the jumper cables and drive away, confident that the 12V will be charged from the drive battery (or should I wait awhile)?
The DC-DC converter (what charges the 12V) can put out a lot of power (125+ amps). As long as the battery is not severely degraded, it should get a decent bulk charge in a fairly short period of time. So yes I'd say drive away as long as you can keep the car in READY mode for 20 minutes or more and get to a secure destination before turning off. Top-off should happen when you next charge the car. Of course the best way to make sure is to put the battery on a dedicated 12V charger and take it to full charge. Once charged, do the load test.
3. Please tell me under what conditions the drive battery will charge the 12V (while charging from the wall? While waiting to charge (timed)? In ready-to-drive mode? Accesories on mode?).
Whenever the main (400V) battery contactors are closed. Basically that's when charging and when the car is in Ready mode. Not when waiting for timer. Also the vehicle will top off the 12V periodically if the car is idle for an extended period (once very 5 days or so iirc). On earlier models this feature was inexplicably disabled if plugged-in. Not sure if that applies to later models.