Car Battery

I have a 1992 Acura, Legend, Automatic, 190K. I had a factory installed alarm system with a passive alarm switch put in and eversince, my car won't start & I have to charge the battery, but it won't stay charged. A mechanic cut some wires which he believed disconnected the alarm system, however this problem continues to happen. I have had to unhook my battery connections which worked, but once I leave them connected for a period of time, my car won't start again & I also seem to have to use that switch to start the car once the battery is recharged.

What is causing my battery to drain? I have taken this issue to two different mechanics & they aren't fixing the problem. I just want everything back the way it was before I had this alarm put in. The company is no longer in business that installed it.

I sure would appreciate some guidance before I once again bring this issue to another mechanic.