I bought my 2008 brand new in Aug. 07 and now have right at 95000 mi on her. Besides all the TSB's and the replacements that came along with them (radiator issue, software upgrades, intercooler, etc.) I had the battery issue several of us had that began with the elusive "Check Brake System" message at 43500 miles.

After replacing both batteries, everything seemed fine but noticed one week when I didn't drive it for about 6 days straight that I got the message again... charged them up and everything was ok. Figured they just drained slowly. Around 76000, the alternator went out on me. Had to replace with factory unit at cost of $475 just for the alternator. Did it myself.

But here's my problem. I occasionally have to charge both batteries up to keep them topped off as the alternator doesn't put out enough juice to keep them charged. Recently got the Dash Command system and can see that my batt voltage will slowly go down over three or four weeks until they are only at 11.6 volts. I'll charge them, they'll be at 13.1 and stay there for awhile, but over a 3 week period they eventually go back down again. Now it's keeping them going for that long, but after about 3 weeks I get a slow cranking engine. Shouldn't this dang thing keep them both topped off? I have the 200 amp H/O alternator, and have had it checked. Working as supposed to. I don't have anything draining them other than factory installed equipment ( I unplug the Dash Command equipment at shutoff ).

It just seems that it's not putting out enough power to keep them charged up, and after 3 weeks I'll have to top them off or I've got that slow cold weather feeling start when cranking her, in the summer even. Any thoughts, similar occurrences with anybody? Or is this normal? Sorry so long, just like to be thorough. Thanks

 

You have a draw somewhere...I live in MA and we have some cold days in the winter, my truck sits a lot as I have a company truck as well and I have never had a battery problem. It is a 2010 and will be needing them soon I would suspect but even after sitting for a week or more it starts fine and I have never gotten any of the dreaded battery messages.

 

We had an issue like this, but not on a ford. it was a gm suv, and the rear window wiper motor was broken, and it was always on trying to move, but couldn't. Don't ask me how the motor didn't just blow and die, or blow a fuse, I don't know. It just sat there and drew power all day and night, causing a dead battery all the time.

I would think that something, somewhere, in your truck, is drawing power when off, and you'll need to find it. If it takes that long to die, it must be something relatively small.