MintyBoost was a terrifically handy DIY USB charger, housed in an Altoids gum tin. It worked great, until Apple changed the way it charged devices, gimping third-party chargers. But have no fear! The MintyBoost team is on the case.
What they found, and what's enumerated in detail in the video below, is that Apple puts unusual resistor values on USB data and power lines. The result is a sort of DRM for hardware, that explains why third-party battery chargers don't always work the way they should: