I'm with sizbut, Eneloop XX batteries and a Technoline BL700 charger, they've been working well in my GPSr and lights for over a year now/
If the Tecnoline BL700 is too expensive, the 7dayshop LCD600 is a suitable cheap (£10) charger with 4 separate channels and a discharge function.
Sanyo Eneloop XX are now Panasonic Eneloop Pro (subject to old stock etc).
The Eneloop XX/Pro are minimum capacity 2450 mAh, but are a fair bit more expensive than the regular 2050 Eneloops (or Hybrios, Recykos etc). Consider whether you'll actually need the extra capacity. If you want to take just 4 spare cells to last a week's cyclyng holiday, they are probably worthwhile, but if all your riding is weekend day rides where the regular cells last easily and you can charge before next weekend, they may not be.
You also don't get something for nothing, and in this case what you've paid for the extra capacity is the number of charge/discharge cycles they will do.
