Nasa BM1 (BT) Bluetooth 12v Battery Monitor
When you need a battery monitor but don't have space for the display or routing the cables would be a nightmare, there is now a solution. The BM-1(BT) will monitor your boat or caravan's lead-acid batteries and transmit the data directly to your mobile phone, or tablet, wirelessly by bluetooth.
A simple Android app, freely available from the nasamarine.com website or Google Play Store, (requires Android V4.3 or later) shows your service battery voltage, current flowing in or out, state of charge and time to charge or discharge the battery. An audible alarm warns if the battery level gets dangerously low. It will also show the starter battery voltage. For apple users a more sophisticated app, with additional features can be purchased from the Apple app store. Compatible with iPhone, iPad and iPod touch. Offers Apple Watch App for iPhone. (Requires iOS 9.0 or later)
The monitor, which draws a meagre 2mA, is supplied with a 100 amp shunt and a pre-made cable assembly to simplify connection to your service battery.