Well, at least some more words of warning:
Be very sure to know what you are doing as the pins that are accessible underneath the battery do not have any protection circuits, iirc.
See also a link to a post by joergrw in the thread I linked before.
Also have a look at the USB pin-out.

In the end, you do this all on your own risk and responsibility.
There may be many subtle pitfalls that may result in sub-optimal behavior or even worse, e.g., components getting hot or the battery not being fed with the right current/voltage may even result in fire or the like.
As another example: voltage drops at components you put in the circuit may result in a too low voltage for charging etc.
So, while there are reports of working configurations, in the end, everyone does this on her/his very own and may experience widely varying results.

So, to repeat: be sure to know what you do and be aware that you do this on your own responsibility.