Sealed !ead acid batteries

[try 1897]

I have two 12 / 12 s and one 12 / 9 ah batteries . Can they be wired together as 12 volts and charged together as one or is the 9 ah one going to overcharge or cause an undercharge in the 12 s ? Help Tom

 

[Frogslayer]

It could work in an emergency to get you home but the 9 amp hour battery will total discharge and start over charging before the 12 amp battery. When running batteries in a series or parallel usually you want them the same age from the same batch and with close resistance values.

 

[try 1897]

Ok thanks. The battery system is not for propulsion but to power a 12 v car radio cig lighter , lights small air compressor etc. Trike with an aluminum trunk . It's a friction drive. Worksman hd with 550lb weight capacity so weight is not a problem. Thanks Tom

 

[bakaneko]

Wait, I am not sure if you are saying that you have two batteries one with 9aH and the other with 12aH? For such a low draw application, you might be able to connect them in parallel. This is just for light application and a slow steady 1-2A charge. I know this is against convention but when two batteries are connected in parallel they become one battery. With low draw application and slow charge, the batteries should always be voltage equalized. You might not get 21aH in total though but better than 12aH.

EDIT: Needless to say, make sure they are around same voltage (<0.5V) before connecting in parallel.