Battery not turning on after being switched off

I had an issue with this 5.2KWh battery yesterday where it discharged from 50% to 4% in an hour with a low load (around 300KW average), and was attempting to discharge to 0% to then fully charge to 100% to re-calibrate the battery, in case this was the reason for it happening.
I turned power off to the battery after trouble shooting after the recharge cycle did not seemingly begin to recharge as set, and now the battery will not turn back on. It powers initially and beeps with lights coming on, only to then beep again and show a red LED briefly on status before turning itself off. Has anyone else had this issue?

There are also 2 messages/warnings on the 'my inverter' - BMS communication error and battery voltage low.

Managed to get it back working in an odd way.
Switched the MCB off to the battery, switched the MCB off to the inverter. I noticed that the battery could power on with the MCB going into the battery was off. I made sure the battery was powered on and then switched both MCBs back on again, to the battery then to the inverter in that order and now it is charging at max power having scheduled a timed charge prior to switching the inverter off.
Fingers crossed.

norse 300KW - thats 300,000 Watts. If that's a 'low load' what is your high load ...