A caution — I just made my annual check through batteries and power supplies, and found the XTAR PB2S 21700 batteries (bought with the device) completely dead. My various other power supplies seem to have held most of their charge for a year.
I would guess there’s no low voltage protection on the PB2S, and it must use a little power all the time watching for someone to insert a demanding device or press the button to wake up the PB2S.
Could be the batteries just didn’t hold the charge that long, rather than got drained. I’ll store them outside of the device starting now, and will check back next year.