Hello again.
3.85V is good. 3.6V is even better. I suggest you print this out, frame it and put it on your wall.
For 2), there is no good answer. If you know how, you can design a good charger but that's a lot of work and requires competence. Another option is getting the original smartphone, that's definitely the easiest way to get the proper charger circuit and proper contacts for the battery. Third option is use some Aliexpress crap which may or may not work and may be lethally dangerous to use.