Demand Energy Equality hold workshops on how to recondition and reuse battery packs (or power banks) and they have quite a good PDF which serves as a primer.
Build your own power bank (website)
Make Your Own Lithium Power Banks (PDF)
They do solar too, and intend in the spring to hold workshops to build solar chargers for refugees (in Greece, where there’s lots of sunlight) - maybe we can host and/or participate in that.
(via an anonymous tip-off)