The HLD-8 (HLD-6P & HLD-8G) is an optional dust- and splashproof battery holder and grip created especially for use with the Olympus E-M5 Mark II. The device can be separated into two parts -- one tailored to shooting in landscape orientation and one that's ideal for portraits.
The landscape unit includes a built-in shutter button as well as a dial for locking the grip onto the bottom of the E-M5 Mark II.
The portrait unit includes a molded grip for stable shooting while the camera is in the vertical (portrait) orientation, a built-in shutter button, two built-in function buttons that can be programmed independently of the function buttons on the E-M5 Mark II body, a DC-IN jack for continuous powered shooting (requires the optional AC-3 Power Adapter), and a compartment for storing an optional additional BLN-1 lithium-ion battery.
When shooting with the E-M5 Mark II and two batteries, you can choose which battery to use first; once it's drained, the camera will start using the second battery for uninterrupted shooting.