This morning I could not start the Stang due to weak battery. Drove the car last 6 days ago, no problem. Did not leave anything on. Suspect the light in the trunk. For now I am removing the bulb.

 

I would check for parasitic current drain at the battery, if possible. First, though, ya gotta know that the battery is still serviceable. Age? Depending on year, the various little "ditties" added to the electronics, multiple airbags, especially, have increased the shut-down battery drain. Early EEC-IV drew about 0.005 to 0.010 Amps., for "Keepn Alive Memory". Today, it may be more.

Some models, Mustang I dunno, but my '04 Explorer uses the PCM to "time-out" after shutdown, any lights left on, like interior courtesy lights, so if you leave a door ajar overnight it won't drain the battery.

 

Found the cause: broken trunk lock. Did not held the lid down. So, the small trunk light was on for a few days. Later, I saw also "Ajar" light on instrument panel when ignition key inserted, though all doors were closed..
I tought the battery was done, but I connected an electronic battery tester to it and diagnosed: "Battery good, charge it". I charged overnight and tested again, battery regained full capacity. So tester paid for itself already.
Yes, I checked the parasitic current drain after removing the bulb and it was just 22mA (0.022A) so it should be normal. The timeout is working on the courtesy lights but not on the trunk light, unfortunately.

 

I went to start mine this morning and no dice. I know if I don't drive it at least once a week it may not start. Since the weather is so cold I'm sure that has a lot to do with battery drainage. However, it is parked in the garage that is heated to around 45-50 degrees. I need to buy a battery tender for it. Any recommendations?

 

I don't drive much either, therefore I keep my Stang on a trickle charger when parked. Harbour Freight has them for $9.99 or $5.99 if on sale

 

I have read that Trickle Chargers are bad for the battery. I ordered a Battery Tender Plus from Amazon. Many stang owners use it.

 

Whoever said Trickle Chargers are "bad" for a battery is full of hocum. So long as the "trickle" is more than the parasitic drain due to Air Bag Power Supplies, Keep Alive Memories, etc., the battery will always be ready to go.

 

Good to know imp.

 

Been using the Battery Tender and I must say it has been a blessing! Especially after not driving the stang for over a week.

 

It has been unseasonably cold for us and my stang was parked for a few days, went to start, it was a no go at first but it ended up starting. I have read that the cd or radio comes on by itself and hence dead battery, so I have removed the radio fuse and will test tomorrow since it has been a few days. Was told battery was good. If not might be battery drain from something else.