hamish pillay

I recently installed a new back up system. A growatt inverter and a Cyclone C5 5k battery. The system was installed in August and in October, while I was away, someone ran the battery down to absolutely zero. To the point of not being recharge with mains or our backup generator. This was previously set up and worked perfectly when we had cable theft etc. I managed to reset the inverter to charge the battery eventually. The problem is that the battery charges to 30% in an hour from base 9% but then to 99% in 30 minutes. In terms of usage - We can run two TVs, router, PC, phones on charge and fans for about 3-4 hours. But so much as a hairdryer switched on and the inverter immediately starts beeping and the battery reads 9% charge. Is the battery salvagable? Is there a programming issue? No one seems to have a clue, not even our installer. The battery supplier wants to remove the battery and return it for testing first. This is a costly exercise too so I am trying to eliminate options before shelling out another few K.