Why will my Battery drain power in 2-3 hours and car won't start?

That theft light is for the Passive Anti Theft System (PATS) that involves the key having the chip in it. You cannot disable that system. A good battery will not drain in 2 or 3 weeks, and should remain good. However, a weak battery or one not fully charging can be succeptable to failure. You mentioned 13.7 volts -- is that at 2,000 RPM or at idle? If you are doing an actual voltage test, you should do it at 2,000 RPM. If it's 13.7 volts at 2,000 RPM, then you have a charging system problem. I would be curious what the peak amperage is that the alternator is putting out. Check all that first. Beyond that, you could have a parasitic draw somewhere causing the battery to drain.