Ive just bought a truck with this setup. Parked in the shade for a few days, and this morning I see all power dead. Measured battery voltage and 6.8V! I would have assumed there is a low voltage disconnect built into either of these systems? There appear to be loads connected directly to the battery.
Is the battery recoverable? Parked in the sun and battery immediately reads 10v and charging.
I assume that you mean the VE Bus BMS V2. That directly controls Victron equipment if you have a GX device and everything is connected. However, it does not control non Victron devices nor does it isolate generic loads, you have to have either relays (Cyrix) or solid state isolators (Battery Protect) connected to the allow to charge and allow to discharge signals off the BMS. See the manual.
Regarding the batteries, you have undoubtedly done some damage to them, the question is how much. When a battery fully discharges the cells often go well out of balance due to slightly different capacity and you may find your 6.8V was made up of a couple of cells at 2.8V and a couple at <1V, which will be more damaged. You may be able to recover some capacity but you would need to monitor closely when recharging and during use afterwards.
The long-term issue is sorting out your installation.
