Just out of the blue here, but would a lithium PSP battery pack be able to power the arduino, if so how and what would it supply?
What is the battery rating?
Usually marked on the casing.
It says 3.6V 1800mAh.
No way... Arduino needs AT LEAST 5 volts. You would need a voltage booster.
Depends which Arduino you had in mind, and at what clock speed.
The arduino Uno, and sorry but I don't know what you mean by clock speed.
"No way... Arduino needs AT LEAST 5 volts. You would need a voltage booster. "
Not totally accurate - a voltage booster is needed, but Atmege 328 data sheet shows 16MHz operation on as little as ~3.9V. You will have to bring that power in to the +5V pin and bypass the regulators.
Boost such as this from pololu.com (on sale this weekend?) would do fine.
Pololu Adjustable Boost Regulator 4-25V
I am using one to boost 5V to 12V to drive strings of 5 LEDs in series.
I have run ProMinis on 3 AA batterys, with voltage from 4.25V to 4.5V.
I have a 3.3V Promini 8MHz running on 3.7V Li Ion battery as a remote control transmitter.