I think these newer 5V USB batteries ("cellphone/tablet re-chargers") are nice development for tapers.
Impressive run times(even with phantom power), low-heat (IME), you can buy these things everywhere - Quickie Marts, grocery stores and big-box retailers.
Cheap, and many options in capacity.
It's a more obvious feature on newer gear (Like the Tascam recorders), but I was surprised how many other, older pieces of gear use 5V.
Some of these don't have true power on the USB feature - just need custom USB>DC jack-in cable to take advantage of these batteries.
A quick study produced this list - and others/additions? Nuances? Deletions? Probably some preamps that might work too?
Creative Nomad Jukebox 3
Tascam DR-100/mkII, DR-60D/mkII, DR-70D, DR-22WL, DR-44WL, DR-2D
Zoom H4n, H5, H6
M-Audio MicroTrack 24/96
M-Audio MicroTrack II