I always keep an extra camcorder battery on hand.  When I'm filming an important event, I don't want to run out of battery power before it's over.  If I do start to run out, I can take my extra battery and put it in.  I take my camcorder everywhere, on vacations with the family, to birthday parties, weddings, and graduations.  Many times I give a gift to the graduate or newlywed couple of the video of their event.  It makes a wonderful gift!  I definitely don't want to run out of battery power in the middle of a wedding or graduation.  Keeping an extra camcorder battery is a great idea.  I have a camcorder case that has lots of little pockets, so I keep extra batteries in it, cleansers, cords and everything else I need for my camcorder.  It's great to have a place to keep my extra camcorder battery so I know exactly where it is when I need it.  I think it's the single most important thing to keep on hand for a camcorder.