Despite repeated attempts the truck keeps telling me update failed because of low battery.
i installed a new 12v battery and keep it ALL on charger every nite but still no go. WTF
Keeping it on the EV charger is of minimal help. What has worked for me is to turn the truck on (with headlights, HVAC off) for about 6 hours in the late evening, have the 12V battery on a battery tender, and let it update at the scheduled 1:00 am.
There are a ton of threads on this already. Do a search on the specific update that is failing (it's probably this charge port one) and read all the other comments about how folks ultimately succeeded.
Also I couldn't help but note your 100-year old truck!
If it tells you it's because of the 12v battery, then it must be. A maintainer can take several hours depending on the SOC to reach the level needed for some updates around 85% SOC or above.
I keep mine on a maintainer all the time and have not issues.
It MUST be connected like this with the NEG connect DOWNSTREAM of the BMS sensor or else the truck will not know the actual battery SOC because it does coulomb counting (detects charge current and uses that as the basis for the SOC).
Also, did you reset the BMS when you put in the new battery?
If not do this:
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VB BMS reset
Make sure 12v battery is fully charged (drive an hour, or after an hour actively charging the HVB)
Start Accessory mode
flash high beams 5 times
step on brake pedal 3 times
red battery icon on dash should flash 3 times
If the dealer changes the 12v battery, they should do this, but they don't always. If they plan on keeping it overnight, there is a good chance they will - Just ask when you pick it up.