Weak batteries???

[04LB7]

So yesterday I use my truck for work all day long with no problems. It was even 27 degrees in the morning and it started up just fine. Get home at the end of the day and park it, come back out to it after it sat for 5 hours or so and all it does is click and flicker the lights when I try and start it. Put a tester on the batteries and it says both are weak!!? How in the hell does two batteries go weak just sitting in my driveway after I've used the truck all day for work?? Nothing was left on because I have nothing in there to even leave on. Only thing I can think of is that the passenger side battery went bad and drained both of them down. I checked connections on both batteries and both are tight. I'm clueless here as to what happened here. Hopefully someone can chime in and shed some light on this. Also if anyone can let me know if replacing the batteries will erase the tune? I wouldn't think it would even hurt the tune, but I'd rather ask to be safe.

[Koho]

Had that very thing happen to mine. Was working all day came back out and did as you described. I threw the battery charger on it, ran it for a bit- came back out and it was dead again. Ended up going down to the dealer and bought 2 new batteries for it. My truck is at 70K thought that was pretty decent battery life as those where the ones from the factory.

[bubblebutt]

Do batteries in pairs , and no won't erase the tunes,

[Hook'em_Horns!]

Originally Posted by 04LB7

…How in the hell does two batteries go weak just sitting in my driveway after I've used the truck all day for work??

Vibration/concussion during the work day finally did in the cell(s) on one battery, and then parking at rest for a period of time was enough for the bad one to drain down the 2nd for a no-start.

More than likely a single bad battery in the pair had a failing cell previously, but the 2nd good one remained strong enough to offset the drain and go unnoticed, which can weaken it over time.

At the end of your work day, the decaying set reached it’s limit after the 5 hrs at rest.

If available fund$ are an issue and you need more time, pull both and charge to determine the single shorted one of the pair.

Replace only the single weakened one of the pair, and cruise on. If in a colder climate, put a timer on your block heater for 1-2 hrs before the morning start is needed, to help the battery along buy reducing the glow plug drain on it.

[04LB7]

Thanks for the quick replies guys.

Ended up buying two batteries and its good to go.

[rms]

What batteries did you get?

I replace my originals with Optimas in July of '09 (at 70k).

Now at 155k. I'll probably be replacing them in the next few months or so.