Parallel Battery Issues

[72k20Farmtruck]

Hey everyone,

I have a 1982 K20 that used to be a 6.2 diesel truck but now has a 99 vortec 454 in it. I’ve noticed lately when starting my truck, it seems to be suffering from low voltage. I do have dual batteries wired in parallel. Both were purchased ~1 year ago, same exact battery. I put my meter on the passenger side battery while the truck is running and get only ~12.1-12.3v, but the driver side shows a proper voltage of 14.6v. So i checked my alternator, voltage at the post of the alternator matches the driver side battery @ 14.6v. I also checked the current on my charge wire, it reads ~1.8-2.2A. Just for reference, my alternator charge wire is a 4awg and is soldered into the battery circuit at the passenger side battery. Could my alternator be going out? Or do we have a battery with a bad cell?
Thanks for your time.

[Getter-Done]

First thing I would do is switch places with the batteries.
Then do the same test,
You may find the issue when you take the batteries out.(Lose wire or???)
And go from there with testing the batteries.

[kwmech]

^^^ yup, loose cables or ground on the aux battery or possibly a bad battery. So like above, swap it out and check

[72k20Farmtruck]

Ok thanks fellas. Will do that and I’ll follow up tonight.

[72k20Farmtruck]

Ok here’s what I found.

Swapped batteries, all connections looked good, re did the grounds and no change. So I put my ammeter on the ground on the low battery and set it to inrush, and cranked the motor over, and got zero amps. So then I checked continuity on both ends of the cable and turns out I’ve got ~2,000 ohms of resistance on that cable. So swapped that cable out and problem resolved! I’ll have to dissect that cable tomorrow and see what caused the failure. Thanks again!

[jjzepplin]

I am in for Cable findings as I have a two battery setup as well.

[72k20Farmtruck]

Ok here it is, textbook battery cable failure.

Just simple corrosion, and an old crimp, looks like one of the original cables. Probably too many heat cycles made the crimp weak, because I was able to simply pull the cable out when I cut the cover off.

[Getter-Done]

Glad it was something simple.

Wiring can be

[72k20Farmtruck]

Originally Posted by Getter-Done

Glad it was something simple.

Wiring can be

Same here! I’m an electrician by trade so it comes easy to me, just sometimes you have to get other opinions when troubleshooting because that helps narrow down issues. Swapping the batteries definitely helped track this one down.