Battery keeps completely dying, need some help

[Q]

2001 Mustang Bullitt. Bout 2 weeks ago, after some very cold weather, went to my car and battery was completely dead. Key fob wouldn't even unlock door type thing. Figured it was the cold + an old battery. Wouldn't jump. Went to store and bought new battery, installed it myself and viola, worked great. Started up even faster than it used to.

Fast forward to today, same thing; dead battery. I drove the car maybe every 4 days since installing the new battery (Mustang is not my DD). Last time I drove was 3 days ago, and it was fine. However on that day when I got in to go home, I did have to crank it 2-3 times before it started.

Does this sound like the alternator? Or something else? Thing that is perplexing me most, is how it is 100% dying (no beeps, electronics, lights work) along with the fact that it won't jump. Now, I haven't attempted to jump this new battery, but I suspect it won't jump either.

 

[MagnusTheBrewer]

Alternator. What does the battery gauge show when it's running?

 

[skyking]

three things are likely:
1) a phantom drain. Easy to test for if you have a simple meter that can be placed inline for amps. Unhook the negative cable, and place the meter inline with the key off and all doors closed. remove the hood lightbulb if so equipped. There should be little to no current draw on the car when parked.
2) bad alternator. This one is less likely, as most cars will show a light on the instrument cluster for it. once again a cheap meter, start the car and check the voltage at the posts. Should be above 14V
3) Loose connection somewhere on the main cables.

 

[BUTCH1]

three things are likely:
1) a phantom drain. Easy to test for if you have a simple meter that can be placed inline for amps. Unhook the negative cable, and place the meter inline with the key off and all doors closed. remove the hood lightbulb if so equipped. There should be little to no current draw on the car when parked.
2) bad alternator. This one is less likely, as most cars will show a light on the instrument cluster for it. once again a cheap meter, start the car and check the voltage at the posts. Should be above 14V
3) Loose connection somewhere on the main cables.

All good suggestions, even a small bulb such as a trunk-light WILL eventually completely drain the battery so I'd go with #1 right off the bat. He can buy a $7 DMM at Harbor Freight that will work fine for these tests. OP, if you see a drain problem, (keep in mind the BCM or "body control module") will always draw around 25-60ma, give it a few minutes to let it get into "sleep" mode. After that if you see extra loss a good method is to go to your fuse box(s) and start pulling fuses one at a time and eventually you will find the power is going out to.

 

[Q]

Thanks all for the suggestions. I'll report back any findings. By the way, the jump was successful, surprisingly.