2005 Chevrolet Silverado 2500HD, Still Have Power After Disconnecting Batteries

I was helping my cousin remove the center console on his 2005 Chevrolet Silverado 2500HD and I was having some power issues. Since we were planning to remove the front seats, I thought we should disconnect the battery because I didn't want to have an air bag light go on. This truck has two batteries under the hood, and we disconnected them both (negatives and positives). But even after disconnecting the batteries, there was still power to the truck. The lights, stereo, power windows, and power seats all still worked. They would flicker and clearly be slower with less power, but they still had power. Why is that? The truck had the batteries disconnected for an hour and there was still power. We ended up not removing the console until we could figure this out. I would appreciate any help I can get. Thanks

Possibly a 3rd battery in somewhere that you don't know about ? Maybe someone got creative with a 3rd battery install. Possibly some big capacitors still wired for an audio system ?. Jim1968 Chevy II Nova Garage Find 2012

1973 Nova Custom

1974 Spirit of America Nova

1973 Nova Pro-Street

I didn't see a third battery. He does have an aftermarket stereo system, but it isn't anything special. Just a stereo, small amp, and sub. It does have the Retained Accessory Power. Maybe there is some extra battery for the computer? This truck has a bunch of electrical gremlins unfortunately...