Battery dies withwin a week.
 

Hello. I've been having this problem with my 67 Mustang for the past few weeks. If I go a week or a little bit more without turning it on my battery is drained and I have to jump start it to turn it on. The batter is about 2 months old so I doubt it's a battery issue. Also, I have an alarm. I've had the alarm on my car for about 3 years and this has never happened before. If I would a week without turning it on it would just take about 2 or 3 cranks to turn it on. Now my batter gets completely drained. What can it be?

Don't rule out a bad battery. Take it to an auto parts store and they shouild check it for free. If its good you may get them to check the alternator. If thats good then there may be a ground or the alarm system may be faulty. I would check these two things first, it should be free.

I replaced my previous battery because of this same problem. By any chance, do you know if Auto Zone or Pep Boys check the alternator?

Most auto parts stores should be able to check the alternator

From the symptoms described its not the alternator. If he starts it every once in a while it works fine, so the alternator is charging the battery for the brief time its running. Somewhere there is a short to ground and you'll have to go looking for it. Is anything else acting funny? gauge? radio? lights anything not working or acting funny is a clue. If nothing pops right out as an obvious problem then use a multimeter and begin tracing the circuits to find the problem.

it could just be a bad battery.

try disconnecting the battery next time you let it sit for awhile. if it still has starting issues then it's more than likely just the battery.

The police have installed a GPS tracking unit that is discharging your battery.... :D

Just kidding...... :D

With EVERYTHING off, Try pulling the fuses out and jumping across the open terminals with a multimeter to see if one of the circuits is pulling current.

This might help to narrow your search.

I had the same issues. Replaced the battery and didn't fix it. Ended up being the alternator. I drive my stang the same frequency as you.

When I drive, it's for a short amount of time, and the battery was doing all the work because the alternator was not properly hooked up and recharging the battery as it should. If I parked at the gym and left afterwards, it was a weak start. When I drove it for 2 hours at night, I lost all electrical. I brought the alternator in NAPA, passed. The issue was I improperly wired the 1 wire 3G alternator where the alternator was not being told to recharge the battery while driving. So while it passed on the NAPA machine, and the battery had lots of life (even though I killed it on the last trip), the wiring was what screwed me. It's also why I always tried to keep it on a charger while sitting. Now I let it sit for up to a month and cranks up just fine with the proper wiring.

Something is drawing current, just like if you left the lights on. Batteries can provide lots of current, chances are if it was a direct short you'd see smoke and flames and own burnt wires. The current is running through something.

The hard part is figuring out what. This can be difficult, especially if troubleshooting electrical systems isn't one of what I'm sure are your many, many talents. But there are basic ways.
There are quite a few things that can fail and draw current. Ignition switch, light switch, alternator, door switches, all kinds of stuff. Some that are always powered and some that shouldn't be.
As said, removing fuses will disable and isolate that circuit. Then you have to wait a week and see what happens. Tedious. But it's a basic way to narrow it down, and that is key.

The first thing I would do is buy a battery disconnect switch. They are cheap and bolt right on the cable and battery. That would allow you to isolate all circuits at once, and it's really not bad thing to have in place anyway. If you install one and the battery still dies... It's the damn battery.
With this switch you avoid losing the charge by disconnecting it when you leave the car.
Then I would go over the car closely to ensure nothing is on. And then do it again. You won't know the problem is gone until you find something wrong. Feel the wires for warmth. Check for sloppy operation of all switches. Make sure the lighter isn't heating. Check the brake light switch. You get the picture.

I don't think it's your alarm, why would it start drawing current after three years? But disconnect it anyway to be sure. And I don't think it's your battery, you replaced it because of this problem.

Study the WIRING DIAGRAMS Get the disconnect switch to make life easier and really look around. We'll be here. Good Luck.

Don't rule out a bad serp belt. They can get dry rotted or loose and not turn the alternator enough to fully charge. If you put your fingers on your belt and the belt turns your fingers black then it's dry rotted. If you have more than 1in "play" in your belt then it's too loose.

Always start with the cheap stuff and work your way up. Belts are like $12 or something.

Keep us posted on what it is/was.

James