On a recent trip (coach delivery) our coach batteries drained down to 8.5V while driving and engine running. Did we damage our deep cycle batteries or are they still recoverable? We are new at this and just trying to learn all these systems. Thank you all.
You can try charging them, but they're probably done or at least damaged.
If the batteries discharged while you were driving you need to check your boost solenoid and its circuit. The alternator should be charging your batteries.
As stated previously stated if you can charge them back up they probably won't have the capacity the once had. Also, when traveling turn off all unnecessary items that are connected to the inverter or if possible turn off the inverter.