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Old 08-12-2019, 03:44 PM
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Matt Shade Matt Shade is offline
Made From Scratch
Join Date: Jan 2007
Location: Ohio
Posts: 2,940
Default How much voltage drop should you see in a battery starting a truck?

Allison has a 2010 F350 with the V10 in it and has been complaining to me for almost a year that it is starting hard. It has a 900CCA gel battery in it that I put in less than 3 years ago and had a 4 year warranty. I have taken it back to batteries plus multiple times and was told each time that it is within spec and they can't warranty it.

I have a 100 amp harbor freight load tester and it shows the battery at 11.8V unloaded and drops down close to 10V with the load applied. With the truck running it shows 13.9 and stays about 12.5 with the load applied. I have not had any trouble starting it the times I've looked at it but have no reason to doubt her when she says she turns the key and isn't sure its going to do anything. I'd say the gauge on the harbor freight tester isn't particularly accurate but the readings jump up to appropriate levels with the truck running.

Today the guy put his meter on and I was able to stand where I could read it and he told me the "battery is gold!, that's holding tight with 1000 amps on it". And while it was just barely catching the bottom edge of the green bar on his tester gauge, it was also under 10.5 volts...He told me he couldn't do anything for me unless I wanted to pay full price for a battery, and that the new one would do that exact same thing this one is doing. He thought I should check my spark plugs.

I made him look at it with my tester on it (knowing I was wasting my time but wtf). He told me my tester was for motorcycle batteries and wouldn't be reliable to a larger battery.

The last idiot I talked to told me that you have to drive an hour before the battery recovers from starting and that we shouldn't make so many short trips with the truck without putting it on a trickle charger.

I'm pretty convinced it has a weak battery. I would have thought a starter going bad would have died by now, and the alternator tests fine. I will probably put a battery in and I will buy it from somebody different.I wanted to see what others thought for how much voltage drop is acceptable though. Is it really ok for it go under 11 volts?
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