The benefits of using a battery grip are twofold. The first has to do with ergonomics. Specifically, battery grips enable you to shoot vertical images far more comfortably using a product primarily designed to be used horizontally. The second has to do with the number of exposures one can capture before needing to recharge, and battery grips double the number of shots you can capture before you need to recharge your batteries.
Vello BG-Series battery grips do all of the above, and at about half the cost of the battery grips sold by the original equipment manufacturers (OEM). Designed for use with a number of popular DSLRs from Nikon and Canon, Vello BG-Series battery grips can store one or two lithium-ion batteries (your camera's dedicated lithium-ion battery plus a spare), which allows you to capture twice the number of exposures between charges. You also have the option of using AA batteries (six to eight, depending on the model). There's a AA-battery clip included with each BG-Series battery grip.
Vello battery grips also feature vertical shutter buttons for improved handling, as well as fingertip controls for A/E Exposure Compensation, AF Point Selector, AE/FE Lock and Index/Reduce. Depending on the model, Vello battery grips weigh between 5.4 and 12 ounces and cost between $45.95 and $74.95, which as mentioned earlier, is about half the price of OEM battery grips.
Vello BG-Series battery grips are available for the following DSLRs:
A useful accessory to go along with the Vello BC-N1 battery grip is the Vello Battery Chamber Cover, which clips onto the battery in place of the original battery tray. The Vello Battery Chamber Cover is also compatible with Nikon’s MB-40 and MB-10 multi-power battery packs.
Please note that with the Nikon D300s only, faster continuous shooting speeds (up to 8 fps) are possible when using the battery grip with an optional EN-EL4A battery and the BC-N1 chamber cover.