This is the 3rd winter in a row I've had trouble with my 07 Lariat. Each winter I have to warranty the motor craft battery. I drive the truck about once a week. Upon trying to leave a three days ago the battery was dead. I jump started it and went on my way. Here it is 3 days later and it won't start. Battery is showing 7.8 volts. I jump started It and while running it was charging at 14.5 volts with around ~30 amps going in to the battery. When I shut the truck off it shows something draining the battery at .5amps. After an hour or two it drops down to 0 amps draw. So my theory of something draining it is a bust. My next thought is maybe the voltage regulator on the alternator is going bad and over charging the battery thus basically frying it. Any other ideas anyone??

 

Are you sure that draw isn't coming back after a while? .5 amps is a fair bit of draw but should be fine if it's stopping. Mine doesn't even draw that much after shutting off with my alarm and remote start (and alarm plus remote start can be a battery hog). Do you by any chance have an aftermarket alarm or start? My truck draws continuous .25 amps but my remote start alarm causes that. I can typically get about two weeks though.

I would have thought your battery would already be toast by now if it was overcharging?

 

If you're on your original battery, I'd say its time to replace it.

 

Did you test the battery?

 

I agree with the others about the battery, I thought I read you replaced the battery but I don't see that anywhere. How old is the battery? Have you tested it? If you're getting 14.5 volts and seeing approximately 30 amps (guessing you've used an ammeter?), you must have a bad battery that's not holding a charge long or a parasitic drain that's returning after the hour?

 

This is the 3rd battery in 3 years. Every winter it does this to me. I take the battery back to ford. They test it, verify it's bad, and warranty me a new battery.

 

Also after shutting the truck off last night I metered 12.5 volts on the battery. After sitting all night its back to 7.9 volts. According to my clamp on ammeter there is no draw off the battery which leads me to believe the battery is just plain bad. But it's only 11 months old. The previous battery only lasted 12 months. Both were ford batteries.

 

I don't think most clamp on meters will measure dc current. Charge the battery up and then leave it unconnected overnight and see if it drops voltage or connect the meter in series (with the truck off) and see what current you get.

It sounds like something on the truck is draining the battery down when it's off. It might not be enough to cause a no start issue but it is wearing out the battery.

 

Did you measure the 30 amps with the clamp on meter? Your alternator might have a bad diode and it's pushing a AC waveform to the battery. That can't be good.

 

My clamp will measure DC amps but if your drain is low enough it might not see it. Also, how cold is it? How long did it charge for (idling doesn't fully charge a battery)? Your battery might be freezing if it's discharged that bad. The other factor is the more you drain it, the worse it is for the battery.

You may have to get a multimeter with DC amps to measure a smaller current more accurately and tie it between the battery and the line. My clamp-on isn't very good at showing my .25A draw. If you were seeing .5amp for one hour then doesn't, that seems suspicious. The BCM does go to sleep but it doesn't draw that much (I don't believe).