Help! Recently I changed the head gasket on my 1992 240x hatch. We put everything back together and now the car won't start without a jump from a battery charger, then the the charger turns off and the car dies. I took the battery to auto zone but they said it was a bad battery. Got a new one with the warranty and tried with that one. the car started at first, but then noticed the Dash board was not working and neither were my lights! I turned the car of and tried again but now the new battery has turned into the OLD one and I need the charger to start it up yet again. I checked the fuses and only the engine control one was damaged (replaced). Any suggestions will be helpful.

More than one issue there likely, you need a good overall mech to look at it. What happens when you let several issues overwhelm you to choke you when you did not fix them one at a time.

It sounds like you've got something staying on/shorting out when it shouldn't be.
I'd check how much current the vehicle is drawing with everything off/key out. You do this with a multi-meter set to monitor current. Put the positive (or negative) cable on the battery, then put one lead on the battery and the other on the other terminal (which shouldn't be touching anything else).