Originally Posted by Alex W
On a diesel engine (and probably the A4 too) nothing will happen if you disconnect power while the engine is running. The battery is only used at startup to turn over the engine.
The batteries also serve as the load source for the alternator. If you open the circuit while the alternator is running, most boats are wired through the battery switch for the alt circuit, you stand a very good chance of blowing some or all of the alternator diodes and destroying the alternator.
Battery switches should not be flipped off when an engine is running unless you've direct wired the alternator to the house battery bank so it always sees a "load"...
The OP ideally needs to cover the switches or physically move them to a safer location.