Hackers love 7-segment displays, and will gladly wax lyrical about the silly words you can almost spell on them and so on. Less appreciated are their bigger cousins, the fourteen and sixteen segment ...

For the 14 segment display, rather than using a 18650 cell or what not, you could use a straight 5v USB battery pack, assuming you get one that'll do 2+ amp out, and use this buck to take it down to 3 ...