12v Battery Suddenly Flat

[DavidMW]

This morning my Leaf was totally dead - had to use the physical key to unlock the door, and display was black. Checked the 12v battery voltage - about 3v so very flat indeed.
Less than 2 days since I'd used the car, main battery was around 50%. Car was locked so presumably nothing should have been draining the 12v battery anyway?
The 12v battery was replaced a year ago by the AA (following a similar experience) who confirmed it was duff. Called out the AA today and they say the battery checks fine so something must be draining it, or there's a fault with the charging system. The local Nissan dealer can't do a diagnostic test before 6 weeks' time! In the meantime I have a charger I could use to make sure the battery is kept charged up but it's pain to do that as we don't have off-road parking.
I've seen a lot of discussions online with owners having similar unexplained problems, but generally quite a few years ago. Has this problem been resolved in recent times?
Any help would be really appreciated!

 

[cornbinder89]

Modern cars, EV and ICE alike have a much higher "key off" loads on the battery than older cars. On ICE they have started making "adaptive voltage regulation" for alternators, no long a "set change voltage" and they also have problems with batteries going dead, but there the symptoms manifest earlier where the car will not crank or crank slowly, alerting there is a problem.
Re charging a Lead Acid battery takes time, and if there isn't enough time on charge, it doesn't matter how big the supply is, it will not recharge all the way and a cumulative under charge will ruin a good battery.
That said, one year out of a L/A battery indicates an on going problem.
5 years is the minimum I consider acceptable for L/A battery life.
Checking for key off loads is the same for EV and an ICE so that is where I would start, well 1st I would remove and clean the terminals shiney- bright, then look for key off loads.
A battery that goes dead in a year is almost always a symptom not a cause. There can be mfg defects that can make it the cause, but they are rare.