Stereo Guys

I had a customer that bought a couple AGM Dekas and a slightly higher powered alternator last year. His stereo worked fine last year but when he was getting his boat ready this year the stereo would turn off when he turned it way up. He has 4 PDX amps running off 2 AGMs and an alpine deck that may or may not be hooked up to his starting battery. He also uses the Remote turn on wire from the deck to the amps. He says the whole thing turns off(deck and amps). The batteries checked out completely fine.

Any typical things I should have him check or thigns that could cause this? I told him to check all his amp connections and go through the deck wiring to make sure it is all good. I didn't tell him but suppose I should tell him to make sure and charge up the starting battery all the way.