My concern is you would want to have the same Ah rating. If not the same amp hour rating, they won't charge evenly and one will draw down the other. I'd only use a matching set of batteries.
Yes they can. I have been doing if for 10+ years on both 12Vdc Minkota trolling motors in fishing boat and sump pump backup 12Vdc motor at the house. Works great as it does what you expect, give you longer run time between charges Go overboard on the gauge wiring between the batteries so current can flow between them. Be advised the downside is if one battery craps out, it will take the 2nd battery down with it as they always are fighting each other to balance out capability. They are hooked in parallel after all. And as others said, use two of the same battery to get that balancing act between the two batteries.
Dissimilar batteries have different internal structures and resulting different internal resistance. Connecting 2 dissimilar batteries "will work" but the charge/discharge cycles will be radically different resulting in reduced capacity of the pair and much shorter battery life for both.
Even small differences in resistance across the bank can result in poor overall performance of the stack. Interconnecting wires between the batteries must be as close to exactly the same length and gauge as possible, for example. Note also the the ground wire of the charge/load goes on one battery and the positive wire from the charge/load goes on the other in order for the internal connecting wire resistance to be the same.
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Lou & Freya the wonder dog
2008 GMC Sierra 3000HD Allison Duramax
2019 Flagstaff 8529FL
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