Things You'll Need
Instructions
Take a battery holder that will hold four AAA-size batteries. Test the holder by inserting four new batteries and connecting the wire leads on the holder to a voltmeter. Make sure you get a voltage reading of 4.5 to 5.12 volts.
Get or assemble an adapter cord with a connector plug that fits the PSP's power socket. The PSP takes a size 4.0 x 1.7 adapter plug. You will likely need to get the connector and a wire to connect it to, both of which you can get from an electronics store.
Connect the battery holder's wires to the adapter wire. You night need to solder the wires or twist them together and secure them with electrical tape. Some wires from a commercial vendor can be connected by just inserting the battery wire leads into the open insulation on the adapter wire.
Insert the batteries back into the holder. Tape them down into the holder to keep them in place if needed.
Disconnect the PSP's battery pack to test your new battery pack. Plug your pack into the PSP by connecting the adapter plug to the power socket. Turn on the PSP. The AAA batteries should power the device.