Most cameras need batteries to operate. Some fully manual SLRs without light meters are fully mechanical, and require no power to operate. However, the vast majority of cameras out there, especially the ones you'll be looking at, require a power source. Your instruction manual will tell you which one your camera uses.

Lithium batteries will last the longest, especially with power-hungry automatic cameras. Always keep a spare or two around, as weak batteries will affect camera performance. Keep your fingers away from the contacts when installing batteries. The oil from your skin may cause electrical or battery problems.

Digital cameras in particular burn through batteries very quickly; small point-and-shoots with no optical viewfinder are the worst offenders. Using rechargeable batteries and always keeping a spare pack as backup in your camera bag goes a long way toward alleviating the short battery life problem. Many SLRs come with their own rechargeable battery. It is a very good idea to buy an extra and have it charging while the other is in the camera.