I feel the same way. In my opinion, it is not possible to replace the battery yourself. It is probably stuck in the thick part of the power cable between the Winbot and the power supply unit. This seems to be stuck.

I put the question to Ecovac, and I'm waiting for an answer. I found the battery on Ebay, but it seems difficult to remove the case. It may be possible to remove the threaded part of the case, which doesn't seem to be glued. I'll tell you more as soon as I get an answer from the manufacturer.