Repair a Denon Heos go pack?

New member here.
Dunno if this is the proper place to ask but here we go:
I have a Denon Heos 1 network speaker where the rechargeable Go Pack no longer seems to charge properly.
It indicates full charge but won't power the speaker if I disconnected the power supply.

So I wonder if anyone tried to take a Go Pack apart and if it will contain a standard battery pack that can be replaced.

I new Go Pack is of course available but they are a bit pricey...

Thanks in advance for any input!