Review on Vidpro PG-6 6000mAh Battery Hand Grip Monopod: A Must-Have for Compact Digital Cameras, Camcorders, GoPro/Action, and Smartphones by Sandra Landgrebe

This item was exactly what you were looking for. This is a tubular battery that is universal. It comes ready to use with a standard screw on top and a threaded bottom. So you can screw on another handle on the bottom or another accessory like a tripod. It has a mini USB charging port and a USB-A output for your device. I am using this for my new iphone gimbal on an upcoming trip. The plan is to keep a few of these in my vest so I can just screw them into the base of the gimbal and charge my phone or gimbal as needed throughout the day. It's light and not big, so it fits very well in a vest. The only reason I didn't give five stars is because I haven't done the trip yet. Although I've tried experimenting to see how well it charges and how long it lasts, it seems on par with other standard batteries on the market.