Regular 220V UPS is not efficient especially if u using Mikrotik or UBQ equipment - 2 battery UPS convert 24V in to 220V than we use adepter converting 220V in to 24V we have massive losses
Someone may have already done it but let me show how to
What u need is
Old non working 2 battery UPS, meanwell AD-55B -this come with build in UPS function
and some cables as shown on the picture
remove everything inside
By the way u can reuse some of the cables - if not u can make new one