Fuse Box overheating

This is for a 2003 Buick Lesabre Limited. The fuse box under the rear seat gets hot and the vehicle won’t crank or start. already checked the alternator and battery which are good but something is killing the battery within 15 minutes of being fully recharged and connected. I did disconnect 2 of the ignition coils which made the fuse relays for ignition cool off. the 2 ignition coils that were removed gave a low green light while the other one was bright. any information greatly appreciated.
Yes the battery was installed properly and Autozone charged it properly it only attempts to crank when hooked up to a big truck and the interior lights stay dim but go bright when the jump pack is connected.

I have a feeling that this is going to require some serious diagnostic work . I also think you should not park in your garage until problem solved.

You might list year of vehicle to help the people give better advice .

I don know what this green light condition is on ignition coils. explain more. .
it seems like something shorted to ground in the circuit.

That should be easy for an auto electric tech to find. That would have to be a very big current drain, like 40 amps, nearly 500 watts. Whatever is causing it will be getting very hot and is by now likely damaged. Are you sure the battery is installed positive to positive and negative to negative? It almost sounds like the battery is installed backwards. Or if the battery has recently been recharged with a battery charger, that may have been done backwards so now the + post is actually the - post.

It’s a 2003