I was never too happy about throwing this loose in the bottom of my frame bag with all the FOD and crud and liquids that might bounce around in there on tour:
So I came up with this:
Not too pretty, and a couple not-strictly-necessary ounces, but it gives me the warm fuzzies. Nice sturdy start button, a 4-pin aviation connector for quick and secure connection, water-resist 2xUSB on the bottom with a rubber cap. Much nicer to throw in the backpack off the bike as a general-purpose powerbank.