78 is actually good news as that can be triggered solely by imbalance, which the BCM interprets as deteriorated capacity; however, it can also mean the pack is complete ****e.
Get your 12V and grounds sorted immediately. If your red battery light comes on with ignition on, but stays off during driving, the car is charging the battery sufficiently. If the 12V is bad, replace it ASAP.
I have a DIY charger/discharger design for under $90.
https://docs.google.com/spreadsheets...it?usp=sharing