Is an isolator needed when paralleling batteries?
Connecting 12 volt lead acid batteries in parallel can be done, but you must be careful to minimize the danger of fire or battery explosion. Yes, manufacturers of diesel pickups connect batteries in parallel to provide the high starting currents required by diesels in cold weather, but the manufacturers take the lowest cost solution to the problem, and figure that the batteries will outlive the warranty period. Batteries can be connected in parallel only if they are of identical age, capacity, and manufacturing lot, and only if they will always remain connected in parallel. If the batteries are ever cycled indepedantly, they should be replaced with another matched pair. If a mismatched pair of batteries is connected in parallel and then allowed to sit, they will pass current back and forth in an effort to ballance charge. If one battery is weaker than the other, it will attempt to drain the stronger battery. Eventually, one battery will short and the other will then dump all remaing ch
