I always custom my own battery packs. Largely depends on which cameras or devices you're running. Most cameras or LED lights that uses V-mount batteries can run between 12v-15v, so a 12vdc output powerbank is definitely usable. However, when it comes to 7.4v-8.4v devices, you'll need a step up/down regulator. Panasonic cameras in particular, their voltage tolerance level is very tight....meaning if the amp draw is high and when your battery is not good enough, there'll be a higher than usual voltage drop and the Panny cams would warn 'This Battery is not usable', and shut down the cam.
Most china powerbanks have overrated capacity readings, and even with that kind of specs, it's usually rated for a single cell output. eg. 3000mah at 3.7v. If it's 10 cells inside, it'll claim 30000mah, but still rated at 3.7v. So once you step up to 7.4v or even 12v, your true capacity ratings at that operating voltage drops significantly.
If you search aliexpress, they also have those USB 5v to LP-E6 battery couplers. it steps up from a USB 5v to 8.4v simulating a AC-DC adaptor, so you can technically use USB powerbanks with 5v 2-3ah output and plug them into your canon cameras like an external power supply.
Just did one mod with the Canon XC10.
https://scontent-sit4-1.xx.fbcdn.ne...=34da58d828557995e9ddc2f31d3beba6&oe=585BD48D
https://scontent-sit4-1.xx.fbcdn.ne...=540a91a585800d4c6c213dab2a2a709b&oe=581EEEB2
Even my previous BMD Pocket Cine Cam was rigged with AA batts.
https://scontent-sit4-1.xx.fbcdn.ne...=866abf44872e100ab8f7ac208e1666e3&oe=582E4C16
My LCD monitors are rigged with 18650 flashlight cells.
https://scontent-sit4-1.xx.fbcdn.ne...=093f2e1dc5eb759b468329df66450385&oe=582938B5
Litepanel SOLA ENG lamp with a custom DIY batt pack, spot-welded together.
https://scontent-sit4-1.xx.fbcdn.ne...=2e818e431eea22222e0e8464364522eb&oe=582579BC