Sparkfun Electronics LiPo ''Fuel Gauge'' Battery Charge Sensor

The LiPo ''Fuel Gauge'' Battery Charge Sensor connects your battery to your project and uses a sophisticated algorithm to detect relative state of charge and direct A/D measurement of battery voltage. In other words, it tells your microcontroller how much 'fuel' is left in the tank. The LiPo Fuel Gauge communicates with your project over I2C and an alert pin also tells you when the charge has dropped below a certain percentage.