Van Junkies offer Battery Monitors from both the Victron BMV range and The Smart Battery Shunts.
The BMV's are high precision battery monitors. The essential function of a battery monitor is to calculate ampere-hours consumed and the state of charge of a battery. Ampere hours consumed are calculated by integrating the current flowing in or out of the battery.
The SmartShunt is an all in one battery monitor, only without a display. Your phone acts as the display. The SmartShunt connects via Bluetooth to the VictronConnect app on your phone (or tablet) and you can conveniently read out all monitored battery parameters, like state of charge, time to go, historical information and much more.