It's hardly a surprise given the United States' new travel restrictions on unpowered gadgets that a lot of people are in the market for a back-up battery.
Unfortunately this is one of the most crowded and uneven product markets in all of tech. Price very rarely matches up with functionality, and for every good idea there are 20 bad ones.
In fact before you take a punt on any of these we'd suggest doing three things before you try to fly to the US:
1) Charge up your phone
2) Stop using your phone
If none of those are possible -- perhaps you just can't kick the Clash of Clans habit while waiting to check in -- turn to one of these for help.
Here are our favourite 8 increasingly ridiculous battery-charging safeguards.