Nasa BM-1 Wireless Battery Monitor
The NASA BM1(BT) Bluetooth battery monitor hardware (sold separately) is supplied complete with a 100 Amp 50mV shunt and all necessary cables to connect to the main service battery. It is intended to monitor a 12 volt lead-acid battery, or bank of batteries, with a total capacity between 5 and 600 Ampere-hours (Ahr).
The information is transmitted using Low Energy Bluetooth (Bluetooth 4.x or higher) and can be viewed on any compatible device running Apple iOS 9.x and WatchOS 2.x.