Keep us posted for the Note8 battery mod .. S7 so far works great I used it with cellular and data plan . Easiest mod and fits perfectly. Not to happy about the charge tho ... maybe because of the note 7 original battery pcb ? charges around 2200 mAh even if it says charged 100% ... Or maybe the app that reads doesnt work well ...
sure as for the pcb, it could be the culprit, how the sot time on average? if it gives like 2/3 time of old battery, then there is definitely a problem
i did similar modification to friends s6 (to s7 battery) as someone did in https://forum.xda-developers.com/galaxy-s6/help/replacing-s6-battery-s7-edge-battery-t3410977 and https://vordhosbn.com/index.php/blog/tech/galaxy-s6-battery-mod-s7-edge-battery/ and it worked just fine so i think that not replacing the pcb on the new battery shouldn't make a big difference
edit: the pcb is not the culprit, you should only use the old battery pcb, about your battery capacity, its like this because your bought battery is fake and actually has just about 2200 mah capacity