Bluetooth battery monitor for smartphones.
Monitoring of 6, 12 and 24 volt batteries possible, power consumption only approx. 6 - 24 mW, reverse polarity protected, no damage to transmitter or battery in the event of reverse polarity, free download from the App Store, Google Play or Windows Store under "Battery-Guard", compatible with iPhone 4S, Android 4.3 and Windows 10 and higher.