I started a new topic for this because I found this Leaf quirk by accident as I was doing some research and experimentation for another topic I started here, but didn't really fit in with it. If anything, this seems to be some good info for those struggling with a dying 12V battery in winter time more than anything.
Some background, being Leaf EV owner since the 2013 model and in all that time, I just assumed that when you press the power button to shut off the Leaf, it shut down most of the devices on the 12V bus right away. Like, before it shuts off the DC to DC converter. I found it, it doesn't actually go in that order. Well at least not on my 2020. I haven't visited any friends yet to check this on earlier models or my wife's 2018 just yet...
This is how I stumbled upon this, interesting quirk. I am in the process of getting a real time power monitor setup inline with my current 12V battery with the aim to measure how much power it uses while sitting idle for hours, overnight, while driving, etc. So I take readings, look at spreadsheets, etc. Now, this is power going in and out of the 12V battery, no the 12V bus as a whole, from the DC to DC converter for example. So last week, while looking over the data, I noticed these weird power spikes. It's not coming from the Leaf DC to DC, but from the battery itself. So further investigation, some massive power spikes were being discharged from the 12V battery in short burst. Enough to make even my Lithium battery fall into the 10.9V range sometimes, which it just never happens with it. At first, I figured it's a really old 12V Lithium and it's age is just showing, but I finally figured out what was happening and what was causing this massive drain.
When I shut off my Leaf, the DC to DC converter shuts down *before* all the other high drain devices on the 12V bus are shut off automatically. I'm referring to things such as the rear window defroster, heated seats, heated steering wheel, radiator fans, cabin ventilation fan, etc. Sometimes there is only a second delay, but sometimes I've seen a few seconds delay. You can watch it happen in LeafSpy sometimes if you are on the screen to monitor the 12V battery current. If it happens to be Night time for example, cold outside, and you have just about everything running on the 12V system (lights included), shutting down the Leaf can cause some power draws in excess of +700 watts sometimes from the battery for a few seconds. Now, I know that good battery can probably handle this brief spike, but I wonder if people that have failing 12V batteries, if this can be a catalyst for depleting the battery enough to fail quickly and be left with a dead Leaf at any random time in the future (day or night).
I'll do more research, but if my hunch is correct and you are one of the unlucky people that need to make your 12V battery last just a little longer until a new one comes in for replacement, the best way to avoid this draw spike is to shut down everything before you turn off the Leaf. So turn off your climate control, heated seats/wheel, rear defroster, lights, etc. Doing this I noticed eased that power draw spike to much, much less power.