@garryjoss @andy-henderson Depending on when you purchased your Flics we did have an adhesive a while which became quite soft over time which made it a bit more difficult to open the battery hatch.
All Flic adhesives have always been washable, so you can carefully clean them with water to freshen up the adhesion. You can rub them with water and maybe even some dishsoap and let it air dry. Don't hold it under water as water may enter and damage the electronics.
Other alternatives are as Andy mentioned, you could use a scissor if you're careful.
We have since changed the adhesive, the latest version is much better than the previous. The adhesives are available separately on our shop.
Feel free to contact our support and we're happy to help you further if none of the above works!