@Scoobyshep we havent installed a backup battery yet.
The MeBay documentation does not specify a particular Battery or a even a voltage.
What is also important is that the Plus terminal off this back up battery is grounded to chassis and the negative terminal connects to E3 on Mebay Controller!
There is a Parameter # 28 in Group 1 listed for Auto start operation, in case of mains failure for the D72 Version
I have absolutely no clue of what ABF is or what they are talking about in this parameter description
If you find any more information Scoobyshep please let us know.