Dead batteries in 04 Duramax 3500

Thanks for all the input. Am pretty certain it was, in the first case, a sticking indoor light switch. The second time I failed to unplug the new camera transmitter at the back bumper. The inside is always unplugged whenever we park it for more that a day. Batteries are new and matching. They always tested good just low. Tested them indivually rather than as a pair so they don't appear to be the issue. In a 04 truck put into service December of 03 there could be additional issues with wiring we aren't aware of. ...yet. So far so good for now. DH has instructed me to fire it up and leave it run 30 min a day every 3-4 days. His thoughts are "If it ain't broke don't fix or and if it moves an inch it ain't broke". That thought process has cost us a lot more than fixing things at first sign but he's old and set in his ways. Big sigh! After 47 years of this you'd think I'd be adjusted to it, but I'm stubborn too.