Advice on sorting out electrical issues

[Canada19]

Hello all,

So I am having some electrical issues. (2009 Avalanche LTZ)

It started off by the avalanche rapidly draining the batteries in the course of about three days. Ordered a battery tester, the passenger side battery was toast, and the drivers side battery was functional but not optimal, replaced both batteries.

Now I have two new 730 CCA batteries in the truck, but when I start the truck, it starts stumbles once and then idles normally. I find this odd as with one useless battery and one sub-optimal battery the truck would start fine assuming I had used it recently. My first course of action was to test the new batteries to make sure they are good.

Drivers side battery 747 CCA 12.54 V (Disconnect from the vehicle.
Passenger side battery 696 CCA 12.39V (Disconnected from the vehicle

This is where it become a bit more confusing for me, in my truck I have an Edge Evolution tuner / LCD gauge screen, when I put the key in the on position but do not start it, the read out is 11.8-12.0 V,

I am confused on how the two barratries are both putting out more than what is read in the truck.

My next course of action is to follow the battery cables around the engine bay, look for wear / tear/ corrosion and any blown fuses. However before I spend a few hours doing that, I figured I would post here to see if any of you were having or have had similar issues, and can point me in the direction of a solution.

Also, tested alternator, it is working optimally with no issues.

Thank you,

 

[ygmn]

dual batteries is not STOCK
so what kit is used?

 

[Canada19]

Hello,

The truck came wired from the dealer with two batteries as requested using the Police Tahoe configuration.

 

[Wpolonavyguy]

I added second battery to my avalanche aswell, knowing have extra amps & battery life helps. I believe I'm going to have to search for paricidic draw something killing both batteries overnight. My blend door actuator has been intermittent, hot air driver side ice cold passenger side.
It's time consuming but I won't pay for labor when I can look just as easily as expensive mechanic would charge.
I hear radio system, door/lights system, & key position select switch can drain batteries.

 

[frito]

I added second battery to my avalanche aswell, knowing have extra amps & battery life helps. I believe I'm going to have to search for paricidic draw something killing both batteries overnight. My blend door actuator has been intermittent, hot air driver side ice cold passenger side.
It's time consuming but I won't pay for labor when I can look just as easily as expensive mechanic would charge.
I hear radio system, door/lights system, & key position select switch can drain batteries.

I too have been having a drain. It's so bad it killed a not too old battery. I first need to replace the battery - again- and then try to track down the drain.

 

[Wpolonavyguy]

I found a thick red amp cable previous owner cut out & must have removed. I'll trace to find other end just to be sure but it's not attached in engine compartment anymore so curious where else they would have taken it?
There was also a small blue wire attached to acc power near left drivers foot fuse panel. I unplugged it just incase shorting wherever it's going probably near other wiring.
A old broken ipod connection in glove box believe going to behind cd/radio plan to remove or upgrade if I go as far as remove head unit.
Will find out soon got too hot today So Cal near palm springs 108 it can wait.
Got my actuator fixed enough for AC I'm happy enough

 

[Wpolonavyguy]

I also wanted to add here is pictures of my volt readings. When the agm battery is fully charged the alternator will quit charging & show 11-12 when alternator charging it can show 14-15 I personally haven't seen it any higher than 15. Likely reading volts. I think Amps would be more useful Guage, I do like having battery indicator.