The max load overall, including the (rider + pillion + floorboard load) recommended is 175 kgs. Keeping a 25 kg load on the floor board is unlikely to significantly impact ride characteristics. The load will have no structural impact on the battery as the battery is inside a protective casing.
Whereas some owners do use their Ather for some heavy duty stuff.
Photo @HarshaVardhan
Photo @frozenprakash
Photo @muthu_km2001