Hey,

I'm having trouble with the battery in my 07 mustang. The battery died, I took it to autozone to recharge it, they told me the battery is fine. And it should be, i bought it pre used only 8 months ago. So i put it back in the car, and within a day and a half. It was dead again, took it back to autozone, they recharged it and told me it was a good battery again. It died the next morning. So i'm thinking alternator, what do you guys think?

Oh, should the dealer pay for this fix? the car only has the 3yr/36000 warranty. Car has 31000 miles on it. Thanks a lot. Im only asking because I currently can't drive the car b/c i tore my achilles tendon; can't drive stick. So later next week ima have someone drive it to the dealer. I want to know what im looking at before i head over there without any information about the warranty.

 

If it's under warranty- let them fix it.

Something is preventing the battery from being charged. An alternator can cause this, as can wiring or a belt. You can quickly check the charging voltage with engine running at the battery terminals. It should be AT LEAST 13v.

 

Not sure about the definition of a "pre-used" battery. I'm assuming it is a "used" battery that someone has deemed to have a useful life without a warranty and sold/gave it to you.
If the batt checks out "good" after a charge, and is "dead" the next day, look for an obvious drain that is occurring while the car is idle. A good time to check for any lighting circuit that may be on, is in the dark. Check the vanity mirror lights in the visors, glove box, engine compartment, interior lights, trunk, etc., to see if any stay on after shutting down.

If there is no visible sign of a light, the next step would be to check for any batt drain to other components. Any faulty after-market radio/audio work can be a drain source. Using a clamp-on ammeter attached to the positive batt cable, check the amp reading. The reading should not exceed 30 +/- milliamps. If the reading is excessive (60 milliamps +), you can pull one fuse at a time to see if that circuit is causing a drain on the batt. If the excessive amp reading drops when you pull a particular fuse, you have located the source of the drain. Unfortunately, some fuses protect multiple circuits making trouble shooting more difficult.

A simple check for a working alternator is to connect a volt meter across the batt poles with the engine off, and note the voltage reading. In theory, a fully charged batt will read 13.2V (2.2V per cell). Your batt should read at least 12V+/-. Using the same connection, start the car and note the voltage reading. It should read 13.8V - 14.2V, if the alternator is charging.

It is always best to make sure you are working with components in a reliable condition. If your batt is failing, confirm the condition by testing it under a load, which is what AZ should have done. Your problem may just be a faulty batt.

 

So, I recharged the battery again at autozone today. I went to a different one. They also told me that the battery was holding its charge. So I did the multmeter test. I'm getting 12.2 volts when the car is off. When it's on im getting 13.6-13.7 volts. So what do you guys think now. Hopefully it will keep it's charge overnight so i can drive it to the dealer tomorow morning.

I'm looking for things that might be on and draining the battery but I can't find anything. I don't have many lights inside besides the two small lights that are above the rear mirror and they are off. I have the stock radio, but it is also off, can it be working in the background and not know it?

 

12.2 volts is about at 50% capacity.12.5 and above is good with 12.7 being about perfect.
http://www.batteryminders.com/batter...0-p-1-c-3.html

http://www.aircraftspruce.com/catalo...er11-11671.php

 

Its been about an hour since i turned off the car. I just rechecked the volts and it's at little below 12.1 volts. What the hell? It's slowly decreasing.

50% at 12.2, wow something is definately wrong with my battery or alternator. I need to figure this out.

 

[QUOTE. I need to figure this out. [/QUOTE]

Time to start pulling fuses, and watching the ammeter.

Your alternator reading of 13.6-13.7 is a tad low. If the reading was taken at idle, rev the engine to 1200-1500 rpms, and see if the reading improves.

A good investment is to own a batt charger. Check for monthly sales at Sears, AZ, etc. for prices. You want an
"automatic" charger ( stops charging when it senses a fully charged batt ). Most chargers come with multi ranges - low - med - start.


"Oh, should the dealer pay for this fix? the car only has the 3yr/36000 warranty. Car has 31000 miles on it."

If the car is under warranty, by all means have the dealer solve your problem.