No power, not battery nor alternator...HELP!!

1998 XJ Sport 4.0 Automatic.

So on my way to work as I'm turning into the shopping center, the radio started cutting out. Then soon after the Jeep shut off and wouldn't start back up. No crank but the interior lights and the radio had power it was weird. Then about a minute after the Jeep started up again.

Then after about 5 hours, I was driving to get some lunch but I had to turn back around because the radio was starting to shut off once again so I got the car back to the parkinglot before it completely died.

So I decided to take the thing over to Autozone to have the battery tested. Battery tested okay and the alternator tested okay. So what is it? What could it be? Could my tiny 10inch infinity basslink subwoofer be draining the power out of my battery? (Battery seems to be original, it looks very old)

So anyway on my way home I just wanted to get second opinion so I went to Kragen but they couldn't do a full check on it due to the fact that they were closing. But they were able to do a quick diagnostics on the electric system and he said the machine said to "Check battery load" so I will be going back tomorrow morning to have the thing tested again. So anyway what could it be?

I'd check the cables. Make sure that the terminals are good and tight, and free of corrosion. Don't just look. Take them off and clean them in case a loose terminal allowed it to oxidize. Make sure that the ground lines are good, and then check the other end of the + cable at the starter for corrosion and looseness.

Also check the strap that runs from the back of the valve cover to the firewall. It can corrode too, but may not show it on the surface.

Also check the ignition switch.

sounds like a plan..thanks for the reply