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Charging batteries in series (different AH ratings)

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  • Charging batteries in series (different AH ratings)

    I just read the Adding batteries in parallel thread. I noticed the original poster had two batteries he wanted to wire in parallel, each of different AH rating. I have known that you should not wire different sized / aged batteries in parallel.

    Stupid question ahead:

    However, if the batteries are the same age, and if the batteries are the same voltage but different AH ratings, would they charge / perform evenly?

    Example:
    Untitled-2.gif

    My batteries are always the same size. However, I wire them in parallel, using only two batteries at most. I have never wired batteries in series. The other thread just caused me to consider the question.
    Paul

  • #2
    It's very hard to get 2 batteries in parallel to share current evenly. As soon as a weaker one develops, it forces the better one to assume the bulk of the load (as battery internal resistance increases) and it wears out quicker, till it is the weaker one, then the stronger one wears out quicker .... .... .....

    With light loads and large batteries, this takes a long time to happen, but as more stress is incurred by the battery bank, the degradation happens quicker.
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    • #3
      Originally posted by Mike90250 View Post
      It's very hard to get 2 batteries in parallel to share current evenly. As soon as a weaker one develops, it forces the better one to assume the bulk of the load (as battery internal resistance increases) and it wears out quicker, till it is the weaker one, then the stronger one wears out quicker .... .... .....

      With light loads and large batteries, this takes a long time to happen, but as more stress is incurred by the battery bank, the degradation happens quicker.
      Would they charge okay in series? I'm confused by your reply. Sorry.
      Paul

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      • #4
        Originally posted by livingincebu View Post
        Would they charge okay in series? I'm confused by your reply. Sorry.
        Batteries in series absolutely need to be identical in design, capacity, and age. Otherwise it is possible to overdischarge or overcharge on of the two batteries, with very bad consequences.
        SunnyBoy 3000 US, 18 BP Solar 175B panels.

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        • #5
          Thanks, I thought so, but was not sure.
          Paul

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          • #6
            Originally posted by livingincebu View Post
            Thanks, I thought so, but was not sure.
            The safe answer for a battery system (parallel or series wired) is that they should all be the same.

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