Basically on my unit there is a UPS device in the headroom of the lift shaft, it charges two 12v batteries wired in series

The UPS has an internal dry relay contact that closes when the UPS internal battery is good, however when the battery in it becomes faulty, the contact will open.

When the contact is open, the ASIXB main board IO plug pins number 1 and 4 are no longer connected, giving the pebobatlow fault.

If you follow your electrical schematics correctly, you'll see that io.1 is 24vdc output and io.4 is your pebobatlow signal, when it's not receiving 24vdc, you'll have the pebobatlow fault.

Either your AXISB board is not giving out 24vdc correctly, your NGL power supply is too low or your UPS is not closing the required contact.