What did you do to your NNBS GMT900 Tahoe/Yukon Today?

[mikeyss]

I chose to do it parallel, simply because the chances of getting 2 dead batteries at the exact same time is pretty much nill, yes you could probably drain both "somehow" but what are the chances?

This is my current situation. I have dual batteries run in parallel, and both are dead. I can jump start it, drive it for 20 mins, and it'll start fine for a few days. Usually after 4 days of sitting, it's back to being dead as a door nail. I even have a mechman 250amp alt, and good copper wire. I've been too lazy to diag it, been driving our 25' Equinox EV for the last few months since the work commute is 6 city miles.

 

[j91z28d1]

my experience with batteries when flat dead is we have a 1200$ recovery pusle charger at work. I've been supised how well it will recover batteries a normal changer can't. but that said it can take over a almost 2 days to fully charge a flat dead battery. if you have 2 battery flat dead in parallel. there's no chance your alternator is fully charging them, you're probably just heating them up more than actually charging with 250amp capable atl and you're lucky it's not just over heating and burning itself up trying. I'd personally disconnect them, change them with something like a cheap 2 amp charger for a day or 2 and then let them rest a day and load test. standard car battery doesn't like being drained flat. you might get one time out it. but 2 or more and I see load testing fall off quickly.

that said, if you don't have a way to measure current drain from that alt. I'd pull the red wire off the alt lug after you drive for a while and before parking it. Alternators can become a current draw as they slowly fail. I almost bought a mechman for my corvette, but there's tons posts about then failing in many different ways. while others have great experience. kinda par for the course with aftermarket upgrades in general. I decided against a 500$ alt and went cheaper but 3 times the work route of making a 220amp off one of the newer trucks work. they are pretty amazing what the new tech can do. being it's a direct bolt on for these gmt900's. I'd never do anything else but a low mileage oem take off for 100$

 

[Doubeleive]

This is my current situation. I have dual batteries run in parallel, and both are dead. I can jump start it, drive it for 20 mins, and it'll start fine for a few days. Usually after 4 days of sitting, it's back to being dead as a door nail. I even have a mechman 250amp alt, and good copper wire. I've been too lazy to diag it, been driving our 25' Equinox EV for the last few months since the work commute is 6 city miles.

I would guess 1 of these things is happening

1. bad battery
2. unknown/unmetered draw/short
3. poor charging
I would start load testing each battery separately, but to me whenever a battery has been drained dead even by accident then it's never the same again
then check charging to each battery, put a load on the system by turning on everything that you can and see what the alternator is putting out to each battery.
if that all checks good then check for a draw while everything is asleep, if there is a heavy draw then starting pulling fuses.