i usually carry two more (because i have them more than necessity), but have only been caught out once where i needed the second. it was an all-day, all night, with the camera on most of the time. for typical shooting, one additional battery is more than enough for the GRDII (the original GRD had less battery life which was why i got my second). i bought the extra battery from my dealer and got the Ricoh one rather than a generic. for the price differential, i'd always rather have the real McCoy.
i just bought a car charger for $20 or so from popflash for my brother who lives in los angeles. if you drive a lot, it makes total sense (it plugs into the lighter and has a battery cradle just like the original charger rather than plugging directly into the camera). however, if you ever shoot out the car window, you'll still want that extra battery so one is always in the camera.
