The Panasonic DMW-BGGH3 Battery Grip for DMC-GH Cameras gives the DMC-GH3 and GH4 longer battery life of more than 1000 pictures when using 2 batteries. It offers comfortable grip and easy handling even in vertical shooting. Three dedicated buttons for exposure, ISO and WB are equipped in addition to the release button on the top as well as the front / rear dials to be used just in the same way of using the camera. This is also splash / dustproof design.
One reason why the Panasonic DMW-BGGH3 is popular is because of its Easy to use