rechargeables and ext batt pack.
can last me the whole day
no need to change batt, recharging only started to slow down at the end of the night when the banquet guests start to leave and the couple shaking their hands.
to save time, i normally just swap the flash with weak batts with my spare flash already loaded with fresh batts.
using 2 550ex and canon ext batt pack, mixture of 2300 and 2500 sanyo AA