Unconnected batteries dropping power...

[Captain Crisp]

Hi one of my batteries manages to drop from 12.70 to about 12.35 all by itself over 10 days. Is there anything I can do, or should I replace? The other one seems to have dropped from 12.70 to 12.65 over the same time. They're both unconnected and sitting in my cellar, so no load.
Also, should I replace both at the same time? I think I read that somewhere...
Thanks and HNY!
Crisp

 

[jwfrary]

Unfortunately that would suggest that it's not in the best of health!

Second ones probobly not far behind. You can get a fair amount for scrap takes the sting out a little.

Lead acids will suffer some self discharge, but that much is a little to much. (Unless its been cold down there!?)

 

[QBhoy]

Cold weather/conditions can do this, I’d say.

 

[PaulRainbow]

"12.70 to about 12.35 all by itself over 10 days" indicates a very poor battery. If these are the leisure bank, i'd replace both.

 

[fisherman]

the man I have used for forty years said charge up to 13.8, leave two days, if drops 2v, knackered.

 

[Daydream believer]

My 3 AGM batteries( all disconnected after charging) were charged to 13.15 in October & still showed 13.05 just before Xmas in quite cold conditions. I have a 5 year old wet cell battery in my shed that I use for starting RC model engines & that drops .5 volt every 5- 6 weeks. The elderly 5 year old 2 wet cell in my launch are always left disconnected & I give a top up charge every couple of months as the drop is very minimal.
So one would expect a battery to maintain its level fairly well, apart from minor fluctuation in temperature .
I would suggest that the OP needs new batteries, & should change both. Possibly keeping the best as a charged spare.

 

[Stemar]

Deleted

 

[jamie N]

This 9 minute video might be of some interest.

 

[Wing Mark]

Hi one of my batteries manages to drop from 12.70 to about 12.35 all by itself over 10 days. Is there anything I can do, or should I replace? The other one seems to have dropped from 12.70 to 12.65 over the same time. They're both unconnected and sitting in my cellar, so no load.
Also, should I replace both at the same time? I think I read that somewhere...
Thanks and HNY!
Crisp

It's often hard to be sure the initial 12.7 was a true reflection of the battery's state of charge.
How was it charged and how long rested?

Some batteries can have a high self discharge yet perform fine in 'normal use'.
Others may drop volts as you have seen, at the same time as losing capacity and cranking amps.

Does it still hold enough charge to meet your needs? If so you might get another season out of it.

It might be useful to charge it up again and re-do the test, and/or do a discharge test running a 'lifelike' load.
Make sure it's properly charged.