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Hi, It's important that the batteries be matched, especially if they are in parallel. Not only do you want the same brand and size, but you might want to ensure that they are operationally matched as well. I do this when buying new batteries for my diesel trucks and tractors. I sort through several batteries on the shelf with a digital voltmeter, looking for ones that are within +/- .1 volt of each other. Then, I take a load tester and load down the battery for 10 seconds - while reading the voltage. I want two batteries that load down to as close to the same voltage, after being close to each other right off the shelf. If the batteries are not matched, then the better performing battery will wind up handling more than 2/3 of the load. Plus, the weaker battery will wind up taking more of the charging current than the good one. This will lead to the premature failure of the 'good' battery. I've seen this occur in as little as two years when parallel batteries were not matched. I find that I can get at least 25% longer service life out of a pair of batteries if I take the few extra minutes to obtain matched ones. Hope it helps. Stan (Electrical Engineer)
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