I'm trying to build a small, portable battery powered USB charger for my android phone. I don't want to use 9V batteries because of their internal resistance and short lifespan. My thoughts were just to use 3V from 2 NiMH or Lithium Ion batteries so a 7805 regulator is out which greatly complicates things (for me at least). What would be the best approach for me to build this while keeping it as simple as possible...and within 20 or so dollars.
