2 batteries but only one charges properly

I have 2 x GE 5.2kWh batteries connected in parallel. I usually aim to charge them overnight off cheap electric and discharge excess solar during the day. One is fully charged, other is around 25% (one of 4 lights on).

How do I realign it so it’s fully charging like its brother?

Curious - writing to this blog seems to have solved it. The power of the written word!