Adafruit (PID 2030 PowerBoost 1000 Basic - 5V USB Boost @ 1000mA from 1.8V+ Synchronous operation means you can disconnect the output completely by connecting the ENable pin to ground. This will completely turn off the output 4A internal switch means you can get 1000mA+ from as low as 1.8V, 1500mA+ from 2 NiMH or Alkaline batteries, and at least 2000mA from a 3.7V LiPoly/LiIon battery or 3 NiMH/Alkalines. Just make sure your batteries can actually supply the required 2-4A, OK? Low battery indicator LED lights up red when the voltage dips below 3.2V, optimized for the most common usage of LiPo/LiIon battery usage On-board 1000mA charge-rate 'Apple/iOS' data resistors. Solder in the included USB connector and you can plug in any iPhone or iPod for a speedy 1000mA charge rate. Works with iPads, both mini and 'classic' type. Full breakout for battery in, control pins and power out 90%+ operating efficiency in most cases (see datasheet for efficiency graphs), and low quiescent current: 5mA when enabled and power LED is on, 20uA when disabled (power and low batt LED are off)