Left on charger in "80% Long Life Mode" but went to 96%!

We went out of town on a family emergency and I left our 2013 Leaf (with a 2017 battery) on the charger. We charge in the 80% long life mode and all charge timers were turned off. I expected the car to charge up to 80% on being plugged in and then do nothing the rest of the time we were gone because there was no charge timer on.

Instead we came back a month later to a 96% charge level! Does anyone understand what happened? Did we just damage our battery health by somehow topping up to 100% over and over?

I thought that with the timer off no charging would happen after the initial, on plug-in charge session (which should terminate at 80%). My only thought is that the charger kept waking up and putting in a little more until it got up to 96% somehow. Or maybe the capacity calibration drifted somehow..?

Thanks for any insights!

Your theory is likely correct. Had you left it plugged in and it hadn't kept restarting, you would likely have ended up with a dead 12 volt battery, instead. Since 96% indicated is really about 90%, I wouldn't worry a lot about that happening in cold weather.

Thanks, that's a relief. Yes I do remember something about it coming on to keep the 12 volt up, and I guess maybe it can't help but charge the traction pack at the same time(?)

It's been averaging around 40F so heat shouldn't be a problem I don't think.

Most people who leave a Leaf plugged in for weeks get a dead 12 volt battery, so it's hard to draw firm conclusions...maybe it's specifically because you had 80% mode on. I remember when I used that on my 2013, with the charge timer set for On/Off at the same time every day, the car would charge briefly if plugged in at that time, even if it had turned off at 80% (actually 79% in my case).