Amazon.com: Synergy Digital Camera Battery, Works with Panasonic Lumix DMC- GH4 Digital Camera, (Li-Ion, 7.4V, 2100 mAh) Ultra Hi-Capacity, Compatible with Panasonic DMW-BLF19 Battery : Electronics
Jupioshop. Battery Grip for Panasonic DMC-GH3 / DMC-GH4 (DMW-BGGH3)
Amazon.com : Synergy Digital Camera Battery, Works with Panasonic Lumix DC-GH5 Digital Camera, (Li-Ion, 7.4V, 2100 mAh) Ultra Hi-Capacity, Compatible with Panasonic DMW-BLF19 Battery : Electronics
Panasonic Battery Grip for Lumix GH3 and GH4 Digital Cameras | eBay
PB-EDGE Battery FOR PANASONIC GH4/GH5 Core SWX | CattsCamera