I have a ctek D250S DC-DC charger in my vehicle charging a 12V 100Ah agm battery from solar and alternator with up to 20A. While travelling I need to charge a 12V 7.5Ah SLA battery. Conneting both in parallel will yield a bank with 12V/107.5Ah, and the charger would be appropriate. However, the charger is not appropriate if the 7.5Ah battery would be connected directly to the charger. The question is whether there is any chance that the charger may "kill" the 7.5Ah battery while being a part of the bank.

Thanks a lot


  • 2
    I'd worry more about the larger battery killing the smaller before the charger even comes into the picture...
    – Ignacio Vazquez-Abrams
    Dec 2, 2015 at 10:49

1 Answer 1


Paralleling batteries causes a world of headaches and battery deaths.

You'd be better off to have a dedicated charging circuit for the 7.5 AH battery and keep them totally separate.

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