Cunawarit, I think you can manage a meeting on one set of lipo batteries easy, nice to have a second set as backup. You can top up between rounds (30minutes?) without upsetting the battery unlike NiMHs.
I would get BRCA approved, whatever lipo you get the improvement will be outstanding, less weight and more power for longer.
Above charger looks good, or for a few quids more one with mains input:
http://www.giantshark.co.uk/power-a6...-p-405325.html
make sure you get all the matching cables you need, a lipo sack may be required. You will be surprised how easy lipos are get on with, do not run until flat or over discharge, always use lipo mode on the charger (if you keep the NiMhs don't mix them up when charging).