MEAN WELL DRC-100 Battery Specifications
The data sheet for the MEAN WELL DRC-100 DIN rail power supplies, with battery charging doesn’t mention any battery specifications.
These power supplies are designed to work with flooded, gel or AGM batteries up to around 20AH.
The capacity of the battery is limited by the charging current, which is 1.25A for the DRC-100B (24V version).
As a rule of thumb, the size of the battery is limited to 10 times the charging current.
This means for a charge current of 1.25A, the battery should be around 12.5AH. You can stretch this a bit to use up to 20AH as a maximum capacity.