Carefully examine the exterior of your battery case and remove any stickers or plugs... revealing hidden screws.
With found screws removed, it's time to use the force to open the enclosure. If the plastic is glued or welded, things may get messy.
"No Serviceable Parts" is a good heading for the picture below. Some of the pegs holding the case together were glued - barnacles!
No worries, a spot of glue during re-assembly will help the medicine go down.
Being mindful of tolerances between parts is important. Manufacturers often set a high priority on making devices slim and smooth; this relief (below) was needed to make room for the battery.
So, be realistic... you may need to shelf the idea of integrating the charging receiver inside the case and fallback to the external sticker.
I was lucky this time, there is just enough room to squeeze-in the charging receiver
The Universal Chargers' flexible PCB has several sets of power and ground pads... use the set that works best with your battery case guts.