My 2006 Ford Mustang worked really well for the first 56,000 miles but now the battery seems to die all the time. If I let it sit for too long, any more than a day and a half, it would need to get a jump to start. The battery has been replaced recently and it was fine when the shop tested it. The alternator is working as well. Something has to be using power when the car is off, but I have no idea what it is. How would I even go about finding out what the problem part is?
From what you mentioned, an electrical test has to be performed for a parasitic draw (something using too much power with car off) in order to determine the issue. The battery is designed to withstand a small amount of draw, which usually comes from the computer, anti-theft device and radio clock.
On your Mustang, Ford has acknowledged that there is an issue in Technical Service Bulletin (TSB) 07-5-13 but has not come up with a fix except to tell you to start your car and let it run for at least 15 minutes a day (partial charge), drive it for 2 hours a day (full charge) or install a Battery Tender (auxiliary charger) which charges the battery when it gets low.
It has also been found that the Shaker Radio units, anti-theft device, aftermarket installed devices and leaving a charger in the outlet socket have contributed to making the battery go bad. Even a new battery can go bad if it has been drained multiple times to need to be jumped.
A certified mechanic, such as one from YourMechanic, can diagnose why your battery is not holding charge and test your vehicle for any parasitic draw.
Before calling someone, you can try the following to see if they help: lock your doors manually, the remote activates the Anti-theft device, make sure there is nothing plugged in the outlet sockets before leaving the car or turn off the Radio/CD player before shutting the car off.
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