Take-away: If you leave your LEAF for any length of time, put a trickle charger on the 12V battery in addition to periodic regular charge. REMEMBER, DISCONNECT GROUND (BLACK) FIRST.
The story: I set my car to charge once a week for an hour and went away for two months. On my return, I hopped in my car and the dashboard was black.
I jumped it, waited a bit and all came back to life, though many of my settings were lost. The dash clock has a set routine, and the console clock eventually gets the time from the GPS (?).
A few days later and 60 miles of driving, it didn't want to start. I jumped it again. (My jumper is a portable jump starter which can work as a trickle charger. )
Yesterday I finally got my level 2 charger installed and plugged it for a multi-charge-day which was to be today. I also left the jumper in trickle mode on the 12V battery.
The dash came on and indicated zero charge, the charger (siemans), indicated "ready to charge ". My other charger was no different. I saw a flashing note on the dash, but could not read it. I heard a thumping sound, similar to the parking brake. Jeez, did my new charger fry my car?
Several times I disconnected the 12V battery, waited, reconnected.
Various things happened: key not recognized, full charge indicated, no charge indicated, thumps. I called the dealer for help several times but they were adament that I had to get the car to them. (Tow: $88 AAA, $180 their recommended company) . $130 just to run diagnostic.
With AAA on the way I tried one more thing, as long as it was showing full charge ... jumper in jump start mode. That did the trick and Thus convinced me it was a bad 12V battery.
The battery was less than three years old and the 84 month warrantee would be worth something. Yup it would! I would save $7 by sitting around at the dealer for many hours (I did not have an appointment). This battery is super easy to change. REMEMBER, DISCONNECT GROUND (BLACK) FIRST.
And right now I'm in the middle of my multi-charge-day. All is good.