Just to clarify, that link refers to the P8, use refer to the P8 Lite guide if you do want to tackle the battery replacement yourself:
https://www.ifixit.com/Guide/Huawei+P8+Lite+Battery+Replacement/95845
But I don't think you should at this point.
Something to keep in mind that simply because you have the battery replaced, that doesn't solve the USB charging port problem. That's probably the issue you need to address. The original battery may have failed, or it may still be fine, but a newly replaced battery or the original battery still need to be recharged periodically, and if neither can receive power that's the source problem.
Your really stuck in a bad place right now. With a drained battery and a bad charging port, you can have the battery replaced but you then need to back up whatever you can before that replacement battery gets drained. Probably doable if you prepare beforehand, but it is a matter of that battery being more or less a one-time usage cost. (not so much the battery itself but the labor charge).
The other part of the problem is with most phones the USB port is soldered to the motherboard. Only some phone do have modular, replaceable USB ports but not many. Most repair facilities will just replace the entire motherboard as a fix for this kind of problem. The internal storage chip, where all your data is stored, is also just an integrated, solid-state, chip also soldered to the motherboard, so when the mobo gets replaced so does the internal storage. And your data goes into a recycle bin too.
So when it comes to the USB port, how does it appear to be damaged? Any way you can finagle it in any way to at least get the battery charged up enough so you can rescue your data?