the previous owner of my '05 c2 stuffed an H8 battery into the tray. To secure it he used the last hole in the tray which is bigger than the other holes. He took the factory bolt (I think) and threaded through a self provided nut (I think). I can't really see any of this because the area below the tray is very, very tight.

When I attempt to loosen the whole assembly the nut just spins around. I've attempted to use pliers and vice grips but the only thing I've managed to do is strip the hell out of the nut.

Now I have a stripped, unaccessable nut holding in a battery that won't take a charge.

WWRLD?

I'm scared (yes scared) of all of the sparks that a dremel would make so close to the gas tank.

 

You could try drilling the bolt head out if you can get enough of a grip from underneath to hold it steady. Or maybe go after the tray itself, mangling it with a drill until you can bend the battery hold down bar back enough to lift the battery out. The tray can be replaced. But the hot drill shards will likely get all over the painted surfaces near the battery tray.

Honestly I'd cut the bolt head off with a Dremel cutoff wheel while using towels as a spark shield.

 

I was able to pop the battery past the lip of the holder with a pry bar. Battery is out. Battery tray has been removed. It was crazy rusty to the point of falling apart. I'm guessing the monkey business with the nut scratched the finish and the oxidation started there. Time for a another battery tray and a big cleanup.

Who sells battery trays?

 

Battery trays corrode due to H2 releases from a charging battery. That is the main reason to use a sealed AGM battery, (however painful they are to find in the right size and their charging reqs.

Battery trays? try your dealer (Part No. 99750415100) or HERE.

 

Lots of name brand AGM batteries available in the correct size (H7) and they have vent tube outlets - if properly vented no corrosion issues. I have an Optima RedTop (sealed) but had to use a tray insert to properly fit. I used this tray insert:
http://www.yellowdogmotorsports.com/details.php?id=104

 

I'm using Optima Red Tops in both my 997s too. It's the 34R size and the R is important as it means the terminals are Reversed from their normal orientation so they OEM cables can reach and connect to them. I originally went to this battery in my silver car to make enough space to house the auxiliary air compressor and control module for the front noselift system. I used a 2nd bolt with large washer in the next hole out to give the OEM hold down plate something to push against when being tightened down and it holds the battery rock-solid in there.