lester12483 wrote:Not true. There is a small amount of energy being used anytime the batteries are connected even with a breaker switch. I know this from experience. If he is gone for 3 months it will drain the batteires fully by the time he gets back.
The only way that will happen is if there is something else in the connections that is draining them, such as contamination in or on the cabling that shorts (even high resistance) one battery terminal to the other, or if there is a power meter that is across the batteries even if the switch to the rest of the system is turned off.
The contamination could be anything from salt to dirt to oil, etc., that has mixed with moisture and created something electrolytic that will pass current. It wouldn't have to be much to drain batteries over a few months. I have seen a lot of dirty car batteries that drain quickly when not in use because of road grit that gets tossed up on top of them, never wiped off, and conducting between the terminals (especially if there is corrosion around the terminals themselves, for some reason).
Just having them series connected but with an open connection from a breaker or keyswitch, etc., will not drain them unless something else is completing that connection in some way.
It's also possible the batteries you had happened to be high-self-discharge for some reason, coincidental to being left connected. Not as likely as the contamination shorting the terminals, but possible.