If you're looking for a small and portable charger, here is a nice (and cheap!) power bank:
https://www.amazon.com/Portable-RAVP...ateway&sr=8-15
I have a slightly different model of one of these with about twice the capacity. But for only $14.99 (after you apply the $1 off coupon the website shows) this is a great deal. eReaders do not have large capacity batteries, and even this small power bank will recharge an eReader a whole bunch of times. RAVpower is a very good and well respected brand too.