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· Registered
Volt, Polestar 2, R1T, Livewire One
1,232 Posts
These are most likely AGM, which are supposed to have very little vampire drain, unlike lead acid. My Bolt and Mach E both have AGM batteries, and I put a deep cycle AGM on my boat.

If you go to other EV forums, like Mach E or Rivian, the same battery issue seems to occur often on those as well. Not only that, but then because of the PAAK (phone as a key) feature, people also complain that the car apps cause the phone batteries to drain too fast. The phone and the vehicle are always trying to pick up a Bluetooth connection.
Only photo I took that has a partially readable label on the battery. Clearly says "AGM" right next to the tie-down on both sides.

I know it's an "AC Delco Gold" with a 36 month warranty.
Vehicle Hood Motor vehicle Automotive design Vehicle door

· Registered
Volt, Polestar 2, R1T, Livewire One
1,232 Posts
I have heard conflicting stories on whether to have a AGM Battery tender or not. If the hummer is sitting for a while should I hook up an AGM battery Tender to it? @Tom E-Tron Tom, your thoughts?
Vehicle Storage
The best way to store the vehicle for any
length of time is to plug in the charge cord
and leave it plugged in. The vehicle
monitors and maintains the 12-volt battery
daily. It is okay to leave the vehicle plugged
in for extended periods of time. Once
charged to full, very little energy is required
to maintain the 12-volt battery and high
voltage battery.
If it is not possible to charge the vehicle
with the charge cord left plugged in, be sure
to fully charge the high voltage battery
before storing. The vehicle will stop
maintenance of the 12-volt battery if the
high voltage battery state of charge gets
too low.
When storing the vehicle on a long-term
‐ Keep the high voltage battery state of
charge at 30%.
‐ Attach an AGM/VRLA compatible battery
tender or trickle charger to the 12-volt
‐ Keep the remote key more than 3 m
(10 ft) away from the vehicle.
12-volt Battery
{ Warning
Batteries have acid that can burn you and
gas that can explode. You can be badly
hurt if you are not careful. Always wear
eye protection. See Jump Starting - North
America 0 344 for tips on working
around a battery without getting hurt.
Do not disconnect the 12-volt battery during
A trickle charger may be attached to the
12-volt battery terminals or trickle charge
from the underhood remote positive (+) and
negative (–) terminals. See Jump Starting -
North America 0 344 for location of these
The vehicle is equipped with an AGM/
VRLA 12-volt battery, which can be
damaged by using the incorrect type of
trickle charger. An AGM/VRLA-compatible
charger must be used, with the
appropriate setting selected. Follow the
trickle charger manufacturer instructions.
With a trickle charger connected to the
12-volt battery, the vehicle will still monitor
the 12-volt battery daily, but it will not use
energy from the high voltage battery for
High Voltage Battery
After extended storage, it is possible that
the vehicle may not operate. If this happens,
the high voltage battery may need to be
plugged in and charged.

· Registered
Volt, Polestar 2, R1T, Livewire One
1,232 Posts
It's still plugged in and it will use the wall plug to maintain battery temp and other checks. It looks to check 12V battery state once a day also.
The Bolt increases the rate at which it checks the 12V battery when it's plugged in. I'm sure the Hummer uses that same strategy but I didn't pay enough attention to it to check.
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