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BradW's avatar
BradW
Explorer II
Nov 10, 2013

Different Brand Batteries in Parallel

I have two M27MF Delco 12v no-maintenance deep cycle batteries in parallel. I have used them this way for many years in our 16’ fishing boat mainly to crank the motor and run the trolling motor. The problem I have is finding replacement Delco batteries when one fails, like happened last week. I need a replacement battery, but can’t seem to find anyone locally who keeps then in stock.

Here is my question: Can I replace the failed Delco with a totally different brand battery (say an Interstate maintenance type battery) and run it in parallel with the remaining Delco no-maintenance battery? Or do the btterries have to match, since they are in parallel?

Thanks for any help,
Brad

17 Replies

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  • RJsfishin's avatar
    RJsfishin
    Explorer
    Nov 10, 2013
    Capacity make no difference whatsoever ! A group 22 will run perfectly w/ a group 31, or even an 8-d.

    Brand makes no difference,....as if a 12v system knows what brand a battery is !!

    Age in itself doesn't make any difference either, only that age usually coincides w/ voltage.

    As Ivylog said, its all in the voltage. The closer the voltage is between paralleled batteries, the better. But even then, only to a point.
  • time2roll's avatar
    time2roll
    Nomad
    Nov 10, 2013
    ^^^^ Depends. When you do get a bad battery put a post up and see what happens.
  • Ivylog's avatar
    Ivylog
    Explorer III
    Nov 10, 2013
    I run eight AMG batteries in parallel of mixed age and capacity... 105 and 110 amp hour without problems. I do check their voltage 24 hours after fully charging and seperating them once a year. As long as they are all within 0.1 volts of 12.7 do you really think I'll replace all eight batteries when one fails that test?:S
    OP, if after a 24 hour rest after being fully charged and seperated they both test the same voltage... do not worry about it.
  • time2roll's avatar
    time2roll
    Nomad
    Nov 10, 2013
    I would try to avoid mixmatched ages more than brand. Both new I might mix them but then you may as well buy same. Nothing wrong with a pair of Costco Group 27 deep cycle batteries.
  • Bobbo's avatar
    Bobbo
    Explorer III
    Nov 10, 2013
    The weaker battery will slowly damage the stronger battery.
  • Bill_Satellite's avatar
    Bill_Satellite
    Explorer II
    Nov 10, 2013
    They don't necessarily have to be the same brand, but as mentioned above the do need to have the same capacity with also means they need to be the same age. If one is gone, you need to replace both.
  • robsouth's avatar
    robsouth
    Explorer II
    Nov 10, 2013
    Generally, batteries in parallel should be the same type, size and age as an older, weaker, smaller battery will draw down a newer, stronger, larger battery to "equalize" the charge so you will not be getting the benefit of the newer battery. Best bet is to replace both at the same time with like batteries.

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