Battery Pack Recommendations
The perfect bank is the one that has just enough power for the battery life you need, while still being as energy dense and compact as possible. Here are the parameters of interest to help you select one.
Look for battery packs that are designed with 18650 batteries internally. These will give you the longest battery life for each charge and will last the most charge cycles. The best single cells on the market are currently about 3350mAh capacity. You can evaluate how good a battery pack is by taking the total number mAh rating of the product and dividing by the cell count or by 3350. Some of the cheaper battery packs use cells that are as low as 2900mAh, which is less energy dense, and less desirable for a compact setup. If you aren't familiar with sizes, I'd recommend staying between 3350mAh and 13400 mAh. Anything larger would be for extended off grid tours. A small 3350mAh pack will give 3+ hours of runtime on level 10 (max) brightness with 15+ hours on level 1. Level 1 is optimized for night while level 10 is optimized for the sunniest time of day. If you need double that runtime or don't like charging for weeks, you can use a 6700mAh capacity.
If you want a specific recommendation, my gold standard for a compact powerbank small enough for cycling, running and hiking is this guy for its size, weight and capacity: http://amzn.to/2pEBG
Each Pro will need a separate USB port to plug into. Each Pro draws 1Amp of current, and almost all ports nowadays are 2A+ rated. Some of the smaller single cell (lipstick sized) power banks are only 1A output, which still meets the Pro needs, but doesn't allow two Pros to run off the same port. You may be thinking... How can I plug two Pro into 1 port? There are a large number of low cost USB power y-splitter cables. http://amzn.to/2qLqUS6