Quick heads up: I finally ended up using a LM 317T to lower the output
voltage to ~4V, using R1=220, R2=550 and a 1uF capacitor, plus a OTB
battery pcb. The phone doesn't get as hot as before, and the "battery"
powers without delay.
https://drive.google.com/file/d/0ByHQWL5Q6bSwTWo3ZnBHTS1KeXc/edit?usp=shari…
https://drive.google.com/file/d/0ByHQWL5Q6bSwM1FPeS1iVlBYX3M/edit?usp=shari…