Dual battery voltage inconsistency while vehicle is on

[BCotrell 10+ year member]

So I was noticing my output has seemed a bit low lately and thought it’s time for a battery health check. Turns out my rear agm needed to be replaced....under warranty...which is good. However when I put the new battery in I’m seeing that I’m at 12.7 with the vehicle on... all while 14.2 at the front battery.

As I was reviewing my ground scenario i realized  that most of my grounds are body grounds and not frame grounds. Could this be the problem as to why I’m not getting 14 in the back or is 12.7 appropriate for the rear. It doesn’t right since the vehicle is on which to me means the alternator is doing the work. This is with the radio down to volume zero.

thanks

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[wew lad 5,000+ posts]

So I was noticing my output has seemed a bit low lately and thought it’s time for a battery health check. Turns out my rear agm needed to be replaced....under warranty...which is good. However when I put the new battery in I’m seeing that I’m at 12.7 with the vehicle on... all while 14.2 at the front battery.

As I was reviewing my ground scenario i realized that most of my grounds are body grounds and not frame grounds. Could this be the problem as to why I’m not getting 14 in the back or is 12.7 appropriate for the rear. It doesn’t right since the vehicle is on which to me means the alternator is doing the work. This is with the radio down to volume zero.

thanks

Yep, everything is in parallel and as such, under no load, they should all read equal voltages. Under load, maybe +-.1-.2Vdc is acceptable

 

[BCotrell 10+ year member]

Grounded my rear battery to front still big difference. Last thing to do is complete front battery to frame ground. After
That I’m out of ideas.