Opening the battery case is easy with the help of a knife fitting between the bottom and the housing of the batteries.

In my case a lot of glue and rubber like material is attached to the battery cell and also to the charge controller board.

Be careful not to use metal tools to remove the white rubberlike material from the board to prevent a short cut, which happend to me.

I yet have to find a way to remove the cells out of the case. Anyone being successful on this alteady ?

Bose used two Samsung cells type ICR18650-26H M

Here is my replacement cell I will eventually order if I find a way to remove the cells from the case.

https://akkuplus.de/Akkupack-fuer-BOSE-S...

they offer two capacities: a smaller with 2600mh for ~ € 20,- and a bigger one with 3400 mh for ~ € 30,-

So this would be still half the price eBay sellers are asking for a replacement battery and way cheaper than Bose.

They will charge you € 80,- but you get 1 year warranty :-)