If you do want to try replacing the battery this page should be a big help for disassembly instructions:
http://www.mobileread.mobi/forums/sh...0&postcount=31
Looks like all you need to do is remove the back cover - much easier than pulling the whole thing apart to get to the screen (it's kinda glued together with double-sided sticky which makes disassembly of the innards risky).
But, can we be sure the battery is the problem? Well, if it's cheap enough I'd say give it a go!
Best of luck.
As to my rationale for not replacing the screen.
My M96 was purchased in 2016.
1) I already did it once (it was tricky to do the first time, and I'm afraid trying a second time might be asking too much);
2) It's 4 years old, probably I will need to replace the battery (and other components) too.
3) It will cost me $100 to replace the screen myself; I'd be lucky to resell it for that much after the repair.
I've replaced it with a 2nd hand Onyx Note as of last week.