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

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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...

Is there a big capacitor on board with the stereo system?

No big capacitor with the stereo system. It is just your standard aftermarket amp set up with the signal wires to the stereo and sub and the power wire directly to the battery. The reason for trying to remove the center console was to replace it with the middle seat. Unfortunately, there is a lot of wiring that goes to the center console (factory amp) or through it to the back, and since it wasn't going to be a straight forward swap, he didn't have the time to change it then. But I think we might try it again this summer, so hopefully we can figure out the power situation. Part of the problem, is that this truck is almost 20 years old and has had so many owners that have added, removed, or modified parts of the electrical system.