Q: Why will my Battery drain power in 2-3 hours and car won't start? on 1998 Ford Taurus

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I have disconnected the battery and left overnight and I was able to start the car in the morning. The Alternator shows 13.7 volts on my meter when charging. Theft light flashes fast immediately after engine start. This is an intermittent problem. The car had just set in my garage for a couple of weeks and now the battery goes dead in three hours. No lights are on, but with the theft system disarmed and the ignition off the "THEFT" light flashed every 2 seconds.
(1) Answer
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.