04 2500 HD Batteries lose voltage at night.

I have an 04 Sierra 2500HD Turbomax Diesel 6.6

A few months back when I would park the truck overnight, my batteries would drain and the truck would not start in the am. I took it to a GMC dealer, and was charged $150.00 for a battery replacement. Told that the good battery was trying to compensate for the bad one and causing them both to drain.
Worked for awhile.
Now I get up in the am, same problem. I charged both batteries and they held a charge 100%. Park the truck overnight. Dead again in the morning.
Took the alternator to an alternator repair shop, they checked it, said it is fine & charging good. Even under a load. Also noticed the air blows cold out the passenger side, but tries to blow hot out the drivers side of the dual zone a/c.
When I drove it about 100 miles the other day I got back & smelled battery acid. Opened the hood & the one close to the firewall was steaming. I have replaced that battery with a new one now. Now I have 2 new batteries. When I attempted to hook them up, the negative sparks on both batteries when I go to hook up the negative post. Is that normal & if not what do I check next. I cannot afford to play trial & error at a GMC dealership. Thanks for any help in advance. By the way I checked to make sure everything was turned off & no lights on when parking the truck for the night. Recently had some new brake shoes put on, & ABS light won't go out, but it is only on when truck is running.Thanks Again. Turkeyshooter.I am afraid to drive it with the new batteries if there is a short some place.

Has the truck went dead since you had new battery put in. If so you may have a draw that is to large for the truck to compensate for. There are test for this and they take some time. Hope this helps.

No. last night was the first night since I put in the new batteries. I cranked up this morning fine. I appreciate the help.
Do I have to take it to a GMC dealer to get the ABS light to go off? My son in law put new brake pads on for me, but did not have the watchamacallit(Thing that shows the codes) to turn off the ABS light. Thanks Again. Turkeyshooter

That watchamacalit is a scan tool which can used at AutoZone for free just ask. But the brake pads should not have caused the light to come on. Could just be a sensor or a lot of other things like a fuse. Have the codes checked the n go from there. Wish you the best of luck.

Try putting a bulb/s inplace of the ground cable, if it/they light up with the key and everything else off pull fuses till the bulb/s go out. Whatever fuse it is might be your battery problem. Keep in mind that the clock, radio, and other 'memory' type items will still draw a very small amount of juice which may make the bulb/s glow dim you are looking for a bright light. This may help I hpoe.