Car battery, unused -how long should charge last ?

mro

Svein_Forkbeard wrote: »

Can I ask why?

So car doesn't get stolen.

It's an 1980s car, easy to break into, easy to steal, has been stolen once & broken into another time.

mro

AdrianC wrote: »

Not a problem, ime.





I'm going to take a guess that the car was sat there unused...



Was that "months later" IN the car? If so, then that's probably your answer. Very few cars that are less than several decades old have no quiescent draw - alarms, clocks, radio memories, ECU memories, remote locking are all consuming power all the time.


I have an old Landy that, quite literally, has zero quiescent draw. Nothing whatsoever using power while it's turned off. No radio, no clock - let alone alarm/remote locking/ECU. It'll sit for a year with the battery (of unknown age and origin, definitely been flattened before) connected, and start first turn. SWMBO's 2cv was in the exact same boat until we fitted a modern radio. Now it needs the battery disconnecting if it's sat for more than a month or two.


One thing lead-acid batteries really don't like is being flat. Properly flatten them, and they very often don't recover properly, especially if they've been left flat.

No, it was a month later (not months), the battery was flat 1 month after being charged.

Battery was disconnected, so no electrics powered, no drain.

AdrianC

Then the battery is !!!!!!ed. Healthy lead-acids will retain charge for ages with no quiescent draw.