There’s a good chance that rapid battery drain on the Touch is the same thing as on an iPhone, namely, Tristar. The Touch 5 does have a schematic available on ZXW but no board views so you are left interpreting the board to determine what is what. It’s easy for identifiable IC’s like Tristar but it’s hard to know which passive s do what.
There’s also the issue that most Touch customers don’t want to spend a lot of money on repairs so it makes micro-soldering work pretty rare.
I’ve worked on a few in the past but with a no fix / no fee business model, it doesn’t make sense to spend a lot of time on them unless data is critical.