It is VERY likely that you simply have a bad battery, as 180 has already indicated. If it is over 3 years old, I'd simply replace it and go from there.

However....
The only reliable way to find current draw is to MEASURE THE DRAW and follow it to it's source. There is only one way to do this. Read on.



Take off one of the battery cables, it does not matter which one but I like to use the positive one.

Set a DVM or Multimeter to it's milliameter scale and make sure you put the probes in the right jacks on the meter.

Now, "clip lead" the DVM or multimeter in series with the battery and cable.

You will see some slight current draw, should be no more than 100 miilliamps. (1/10th of an amp)

If you see more than that (and if it really IS current drain and not a bad battery you will see 150 to 500 milliamps) then start pulling fuses from the box under the hood until the drain goes down to well under 100 or to zero. When you get to the fuse carrying the offending current, you will know it!

(I do not tell you to pull fuses from the box in the dash, as those fuses are fed by switched power from the key - all of them, I believe. If none of the underhood fuses stop the current flow, go ahead and pull the ones in the dash if you want to, but I am certain they are all switched by the key - but I've been wrong before, so try them if you need to.)

This won't FIX the problem, but it will tell you about where the problem is. The fault MUST be beyond that one fuse. Go download the service manual, or at least look in the owner's manual to find out what that particular fuse feeds. If you need help at that point, I'll be back on here later today.

If you cannot get the current to stop flowing with all of the fuses out, there are few options left but you probably have leaking diodes in the alternator (there is no fuse in this lead). Remove the heavy red wire from the alternator and keep it insulated from ground! If your current goes down, replace the alternator. If the current does not go down, there are few options left. But let's deal with that not-very-likely possibility only if we go that far.


Some notes:
If you allow the red lead to the alternator to touch ground, you will blow the fuse in the meter - or destroy the meter if it is a super-cheap unfused type.

My personal experience is that any battery with more than 30 to 45 milliamps of draw on it (.030 to .045 amp) will discharge in a week or two, less if the battery is old and weak. I have seen police cars with 100 milliamps of draw drain their battery in two days, but by putting a new battery in, the battery is good for a week or more.

Large storage batteries like in cars are designed to supply several hundred amps for a few seconds, but, oddly enough, they DO NOT like to provide 1/2 amp (500 milliamps) for even a few days. They simply are not designed for that. If you have an aftermarket audio amp or other item connected to battery, it COULD be operating normally but drawing too much standby current. Placing a relay in it's power lead that is keyed by the ignition would solve this problem.

Whatever the cause, by allowing the battery to be discharged like this a few times, will have degraded it's life considerably. Such batteries as in cars do NOT like to be fully discharged like this! When you get this fixed, it will probably be time for a new battery.