Power Rails (Game Boy Advance SP)
The power input (VCC) to the system comes from the battery, through the F2 fuse and into the power switch, out of pin C, then to the power regulator and low battery detector.
Depending on revision, earlier revisions had a power regulator (U4) and pin 4 is the VCC input (from the battery).
On newer revisions it has an integrated single PMIC (U3) and pin 36 is the VCC input (from battery).
An important note is on the schematic the VDD5 rail, and P2VDD are labelled and go to 5V rail on most revisions of console.
However, on some revisions it is 9V input and linked to P2VDD.
The safe pin that is always joined to 5V on all revisions is VSHA (pin 31).