A circuit includes a first analog to digital converter configured to convert an analog voltage sample of a rechargeable power source into a digital voltage value, a second analog to digital converter configured to convert an analog current sample of the rechargeable power source into a digital current value, a charge state controller configured to determine a charge state of the rechargeable power source based on the digital voltage value and the digital current value, and a communication interface configured to output a computer-readable indication of the charge state. The charge state controller is further configured to receive pregenerated voltage values and pregenerated current values, and determine a simulated charge state of the rechargeable power source based on the pregenerated voltage values and the pregenerated current values. The communication interface is further configured to output a computer-readable indication of the simulated charge state.