Li's have a finite lifespan that starts the day they are fabricated. They degrade if used... or stored.
See where the OEM cards was made.This?
Not sure if I can trust those on EBay or AliExpress...
The S7 Edge and XPower mods sound interesting as they give you extra capacity, but the guidelines I found are mostly textual, some video/photo instructions would be nice.
No problem. But how can you know where they're from when buying online and if they're legitimate, unless you're buying directly from LG?
Try to find a LG approved parts distributor.
It's a b*tch to do even for a Samsung.