connecting different AH batteries in parallel

Discussion in 'The Beginner' started by jenny and mitch, Oct 22, 2010.

  1. jenny and mitch

    jenny and mitch Funster

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    Ok folks, need to know the technical "yes or no" to adding an extra battery to the leisure system if it has adifferent AH rating . I dont mean a110 going with a 75, but say a 75 with an 85. Also could an automotive batt be coupled to a deep cycle leasure batt ? PS. The Tronix T4X charger from Aldi is superb and at only £9.99 a steal. Thanks in anticipation. Mitch.
     
  2. Wildman

    Wildman Read Only Funster

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    when two batteries are connected they both take the characteristics of the lowest rated. So a 75 +85 would only charge as a pair of 75's. Deep discharge and ordinary batteries have other problems as deep discharging an ordinary battery will kill it.
    The only safe way is to buy a pair of identical batteries, never replace just one.
    Having said all that many people do mix batteries, how long they last like that is another matter. The old battery will eventually kill the good one.
     
  3. Douglas

    Douglas Read Only Funster

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    different AH is not a real problem but different types are, also different aged/used is also unwise as they are in different conditions and have different charge and discharge performances.

    Doug...
     
  4. jenny and mitch

    jenny and mitch Funster

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    AH difference

    Many thanks Roger and Doug , hand in pocket then.:cry:
     
  5. jonandshell

    jonandshell Funster

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    I wouldn't worry about it. The different capacity batteries will both charge and discharge at the same voltages. All it means it that the larger battery will do most of the work.
    Remember, voltage is only electrical pressure. As long as both batteries are in parallel, they'll sort themselves out and you'll never know what is happening.
    For instance, if we exaggerate the scenario, if one battery is 50Ah and the other is 150Ah, for a discharge of 8amps across both batteries in parallel, one will be discharging at 2amps, the other, bigger, battery will discharge at 6 amps. It's all about how the electrical pressure (voltage) is maintained equally across the two batteries in parallel.
    As for charging them, both batteries are subjected to the same charging voltage and the bigger battery will draw more of the charging current in exactly the same proportions as the discharge scenario.
    As long as both batteries are connected in parallel, and both in good condition, you'll have no problems.
     
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