Ive tried 4 different batteries so the odds on all 4 being faulty id have thought are slim.
After on/off switch and general fiddling, so far after 5-10 mins i can get it to come on and work. Once working it generally stays working.
That said on dive 1 today on the dive i got a brief (2 second) flashing red LED but then went back to green and stayed there.
Im not getting any audible alarms here with this at all. Ive inspected and checked the moisture probe pins and they look fine. No obvious signs of corrosion on the wires of PCB that i can see (its a newish housing).
Admittedly i havent taken the entire system out of the bulkhead to inspect yet as im on a boat with limited tools and time so maybe that'll be the reluctant next option.