Ok so the backup battery was totally dead, replaced it with a new 3V 2025 battery just like the one in your picture...
Cut the main battery open got the old batteries out and temporarily connected 4 AA batteries [2100ma] ones....
The consult when holding the on button still won't power up... Tried holding left and right squares down... Nothing... There is power coming from the batteries but the consult won't display anything...
I got a 6V DC charger with the batteries unconnected can see a voltage at the pins so the power is travelling from the dc port to the battery terminals ok.
All the ribbon connectors appear to be fine and the pcb components don't appear to be burnt out....
Did I miss something?