There are probably a dozen different brands of USB external battery packs that are equally good. I'm satisfied with the Jackery USB battery. Got one last year based on recommendations from a friend. Works great and it's solid. I've dropped it several times, mostly on pavement from handlebar height because I'm a klutz and the USB battery packs are shaped like bars of soap just asking to be dropped. Barely a nick in the cover, keeps on working.

So far my only USB rechargeable devices that can't be run and charged simultaneously is the Light & Motion Urban 500. Plugging in a battery pack puts it in standby recharge-only mode. Too bad, it's a great light otherwise.

All my other USB lights, smart phone, flip phone, video camera, etc., can run and charge simultaneously. I got a tiny, lightweight USB battery pack, about the size of a cigarette lighter, just to mount on my helmet to enable extended run time with my video camera when it's mounted on my helmet. When I run the video camera on the handlebar I'll hook it up to the Jackery and it's so efficient the camera is often fully charged by the time I get home while simultaneously recording my ride. The smaller, cheaper USB batteries aren't as efficient.