"jurepu" mention his way of switching between external and internal batteries. My way is this:
I am using here little connector which can be found on some old computer parts or can be bought in electronical store and tiny switch I bought from DX as PSP spare part. Wiring is easy. I only cut in half the positive internal battery wire to solder it on switch and add there only two extra wires for external battery. On the photos there is not the magnets on camera yet, but I am going to add them there on the camera. Magnets are also on external battery and there I ad connector to fit one I aded on camera, so I can not connect the external battery wrong way if I made wiring correctly. Switch in position one means that the internal battery is working, in position two means that external battery can be connected. And yes it also resets internal clock every time the switch position is changed. Connector and switch on camera I aded are hot glued.
What do you people think about my way?