Some good ideas, I have made a home made Lithium ion battery pack
that can take 400 (I have tested) all flash shots with LCD preview
before it needs recharging (guess 600-800 normal photo's) if you
would like to know how to make such a pack etc let me know. The
battery is quite small and velcros to the camera strap.
Ok...here goes....I'll give you a brief run down, and if you need more details on a particular part, let me know.
Cruise around Ebay looking for some Lithium Ion laptop batteries, brand new ones are preferable, but good condition used should be ok, I have used dell but Acer (containing Sony Energytec lithium cells) seem to be better, break them up carefully to remove the cells. I will assume in this text that you are using the Sony cells, they are rated at 2700Mah each, and are 3.6volts, so simply put two in series. Try not to solder directly onto the terminals, use the spot welded tags that are already there, so as not to heat the cells too much, solder quickly!
Tape the two cells side by side and attach some velcro to them (good quality stuff) and solder on a socket or plug (the type that can't be pulled apart without unclipping, radio control car battery connectors are a good source). Put some velcro on your camera strap to attach the batteries with.
The next part you can do in two ways, 1 is to buy an Olympus spare battery cartridge and drill a little hole in the bottom to feed the wires from the battery, the other is simply to plug the batteries into the AC adapter port but this is a little clumsy (but cheaper).
As far as re-charging the cells, look for a cheap generic Lithium (HAS to be lithium!!) charger on Ebay, I got a Rayovac for $10. Check the polarity before you connect the cells, or you will damage the batteries and/or charger.
Out of one Acer laptop batterty I managed to get 6 cells, this is enough for 3 lithium packs, at 600 shots a pack, that is 1800 shots!! and for around $15, a lot cheaper than the Lipo.
If you think you maybe going on a mega shoot in the future, you can connect a number of cells in parallel and then put two of these sets in series, in this way you can make packs that will be good for 10,000 shots!!
Have fun and ask me if you need some more details.
Chris
I will try and post some shots of my setup soon.