This could apply to any of the Duos but I will be specifically concerned with the 2300 so that's what I shall discuss.
I will need to replace the internal batteries on two battery packs, so I will probably take pictures and provide useful information, and also ask before I do it for any pointers.
First I had to look up what kind of battery it was. The 2300 uses a ...let's search, shall we? the answer is elusive.
Anything here? No, that is for Type I batteries. But there's a link -