I checked the voltage in both of my batterys yesterday and they both were 11.84 volts. This is after sitting for 3 days. The truck starts good and charges in the 14 volt range or 13.9 as checked with a meter. After driving the batterys both read 12.5 volts. This morning back to 11.84 volts.I was always told a battery is in the dead range under 12 volts. Anyone got any hints?I did just recently have a jake brake installed in the truck and they put a lead to the battery + side for the power to it. In that configuration power stays on to it all the time. I don't know if I had this condition prior to installing the jake.Truck runs great so I don't want to start digging around if not necessary.Thanks for any help scram06

Batteries completely charged are at 12.6 Volts... Normal charging range is 13.5 to 14.5 typically.So if the batteries are slipping to under 12.0V after a few days its time to replace the batteries... Both of them at the same time!

You may want to movethe exhaust brake lead to a switched source to stop the constant drain with the key off.

You may want to movethe exhaust brake lead to a switched source to stop the constant drain with the key off.

D'Oh! I missed that... Good catch...

Depending on the exhaust brake it may not use power, my Jake goes to the battery direct and my truck can sit for 8 weeks without a battery issue, it's just giving a relay the positive for switching. I would guess time for new batteries. Sears Platinum's are about the best thing out there.

I hated to do it but all they had at the auto parts were Motorcraft when I changed mine.

I hated to do it but all they had at the auto parts were Motorcraft when I changed mine.

Thats okay.. my buddy has my OEM's in his '00 F-250!

Turns out my trusty Craftsman meter is on the fritz. I checked the voltage with my neighbors expensive meter and got 12.55 in both batterys. I never thought my meter would give error readings. I thought it would just die one day and that would be the end of it.I was ready to start digging around on a perfectly good system! All is good, thanks for the help anyway!scram06

Crown Batteries are the only thing you will find in my vehicles. Simply the best money can buy IMO :thumbup2:Don

12.55V isn't exactly a full charge either. 12.6 to 12.8 is a good full charge...Anything under 12.0 is basically dead...

There are other parsitic drains as well. I found my batteries dead (no start) after an extended time parked. Batteries recharged fine & passed load test. I cleaned all the terminals just in case. I have a solar battery maintainer (had to repair a damaged lead) which I set on the dash & plug into the bottom 12V accessory plug (on all the time). I don't know if all electrical meters have them but all the ones I've ever owned had batteries IN THE METER.