Battery capacity dropped by 90%

I have two Gen 1 inverters each with a 5kWh battery. One of the batteries capacity has dropped to 500Wh from 5kWh, so only 10%. I have no idea why.
Any advice on how to reset it back to 5kWh.

When did you last do a calibration?

Start with scheduling a calibration. Then pick up the phone and head to twitter with a message to Octopus.