rallantando

I'm a novice boater and recently acquired a narrowboat. She was running completely smoothly, including two cruises, until this weekend when the batteries have stopped working. Everything works fine when the engine is running, but as soon as it shuts off everything (including the inverter, charger and 12V system) turns off. Looks to me that the batteries are not holding charge but not sure why this would be. I did accidentally run the batteries completely flat, but have since run the engine for about 10 hours to fully charge but they're not taking. Any help? Specs: - 5 x 200Ah Victron GEL Deep Cycle Batteries - 3Kva Victron Phoenix MultiPlus 12/3000 Inverter Charger - Victron 3600W 230v Isolating Transformer