GitHub - sparkfun/Photon_Battery_Shield: Battery Shield for the Spark Photon. Has a charging circuit, as well as a fuel gauge.
Lithium Ion Battery - 2Ah - PRT-13855 - SparkFun Electronics
SparkFun Electronics, Inc. - Don't miss out on our Deal of the Week! The SparkFun Battery Babysitter is half battery charger, half battery monitor, and all you'll ever need to keep your