In reply to davidbeynon:
not on the grip i have, the grip plugs into the battery compartment and then 2 batteries go onto a tray inside the grip. the camera will run fine on one battery in the grip so you shut down swop the batteries over and slot it back in, a process that can take as little as 10 seconds with practice. assuming you have more batteries available.
without the grip you need to take the camera off the tripod, change the battery and then remount on the tripod. while i think you can do that fairly quickly, you'd need to do that roughly twice as often (because the grip holds two batteries)
if you are doing very long time lapses it should be possible to swop battieres without most people noticing in the end result.