Why would you need it? For the most accurate battery system monitoring, a separate battery monitor that directly attaches to a current shunt like Victron Energy's BMV-712 Smart model is the way to go. While Victron charge controllers do provide charge & system monitoring, they do so based on the voltage going into the batteries. True accuracy comes from measuring current/amps at the battery bank.
How do you install it? The BMV-712 Smart Battery Monitor comes with the current shunt that connects at the battery bank (via battery cable & fuse included), which you then connect to the BMV-712 using a standard RJ12 phone cable (included). You can then flush mount the BMV-712 or mount in one of Victron's tidy enclosures where it is convenient for you to view.
Bluetooth-Enabled! The BMV-712 Smart Battery Monitor is Victron Energy's latest model which includes built-in bluetooth functionality so that you can easily pair it to your smartphone. Bluetooth also allows the monitor to communicate with other Victron products.