On the face of it, a digital slr battery grip might not seem to be the most useful camera accessory, but once you've used one you might just change your mind! With many modern digital cameras having a greater range of power hungry features such as image stabilisation or LCD screens in addition to powered auto focus systems, having an extra battery installed in your camera and ready to use is very handy. You will double the battery life and therefore approximately double the number of shots you can take before recharging. Canon, Nikon, Pentax, Olympus and Sony all offer battery grips to fit their digital SLR cameras. Most camera battery grips include a vertical shooting facility, making it much easier to use the camera in 'portrait' mode.
The camera can photograph thought. It’s better than a paragraph of sweet polemic.
—Dirk Bogarde (b. 1921)
In most cases, the camera controls are duplicated on the grip so that rather than having to 'twist' your wrists to use the shutter button, you can use the shutter controls on the battery grip to take your picture. Once you get used to having this extra set of camera controls it's hard to go back to using the camera in the conventional way! As digital slr cameras are designed to be ever smaller, the addition of a battery grip provides a little extra surface area for better camera handling. This makes it easier to steady the camera properly, and should help control camera shake, particularly if you regularly use a telephoto or longer zoom lens. It is important to choose the correct battery grip for your camera as they are not usually interchangeable. Canon battery grips for the EOS camera lineup include the BG-E3 model which will fit the Digital Rebel XT/Xti range (EOS350D and 400D outside of the USA), whilst the BG-E2N fits the recently released Canon EOS40D model. If you own the full frame Canon EOS 5D model, you will need the BG-E4 battery grip. Nikon digital SLR owners can also buy a specific Nikon battery grip to suit their camera.
If you own a nikon d80 camera, you need to buy a Nikon MB-D80 Multi-function Battery Pack, whilst owners of the Nikon D200 camera will require the MB-D200 grip. Fitting a battery grip to your camera is very straightforward. In the case of my Canon EOS 40D it took less than 5 minutes from start to finish and simply involved removing the battery compartment cover and attaching the battery grip with one large knurled wheel. To sum up, a battery grip will add a little weight and extra size to your camera, but the advantages are so much more than just having an extra battery installed. In fact, once you've installed a battery grip on your slr camera I doubt that you will ever want to remove it!