Why Do I Need A Battery Monitor?

You can make many upgrades to your battery system, but one of the simplest and most useful is adding a battery monitor

One of the most basic functions of a battery monitor is to display the remaining charge of your battery system. A BMS collects data and uses it to optimize each individual battery. However, a battery monitor collects information and displays it so that you can optimize the performance of your entire battery system. Battery monitors do much more than just display the state of charge of your system. Your battery monitor also provides you real-time and historical information on voltage, power consumption, temperature, and more. This data allows you to make better decisions on how to optimize your battery usage and charging. 

In lead-acid batteries, the battery voltage drops significantly as you use them. This voltage drop typically gives some indication that your batteries are running low. This relationship between voltage and SOC depends directly on the battery technology used. As an example, the diagram below compares the discharge curves between a Lithium-Ion battery.

lithium voltage chart

The diagram below shows that the voltage measurement difference between a DoD value of 40% and 80% is about 6.0V for a 48V battery in lead-acid technology, while it is only 0.5V for lithium-iron phosphate !


discharge curve lithium ion diagram

Lead-acid batteries have a relatively linear curve, which allows a good estimation of the state of charge: for a measured voltage, it is possible to estimate fairly precisely the value of the associated SoC. However, Lithium-ion batteries have a much flatter discharge curve, which means that over a wide operating range, the voltage at the battery terminals changes very slightly. Lithium Iron Phosphate technology has the flattest discharge curve, which makes it very difficult to estimate SoC on a simple voltage measurement. Indeed, the voltage difference between two SoC values may be so small that it is not possible to estimate the state of charge with an acceptable level of precision.

Without a battery monitor you will not know when your batteries are about to shut down. There is no warning that your batteries are almost depleted until it’s too late and the BMS shuts them off. 

Victron Energy have a great range of Battery monitors and accessories to suit.  Added to all this is the free and ever popular VictronConnect app, plus the VRM Portal (also free) – where device monitoring, product configuration, firmware updates and data can all come together.

This BMV (Battery Monitor Victron) range are a group of high precision battery monitors. Their essential function is to calculate ampere hours consumed and the state of charge of a battery. Think of these monitors as your battery ‘fuel gauge’, with a time-to-go indicator and much more.

BMV 712 Smart:

Victron bmv 712 battery monitor

Victron Smart technology simplifies system setup, monitoring and firmware updates using the free VictronConnect app.

The **2 in the product name refers to the fact this product features a second input which can be programmed to measure one of three things ,Voltage of a  second battery, battery temperature, or the midpoint voltage of a battery bank.

Other features:

  •  - Battery voltage, current, power, ampere-hours consumed and state of charge
  • - Remaining time at the current rate of discharge
  • - Programmable visual and audible alarm
  • - Programmable relay, to turn off noncritical loads or to run a generator when needed
  • - 500 Amp quick connect shunt and connection kit
  • - Shunt selection capability up to 10,000 Amps
  • - VE.Direct communication port
  • - Stores a wide range of historical events, which can be used to evaluate usage patterns and battery health
  • - Wide input voltage range: 6.5 – 70 V
  •  - High current measurement resolution: 10 mA (0.01 A)
  • - Additional input to measure voltage (of a second battery), temperature or midpoint voltage, and corresponding alarm and relay settings

SmartShunt 500A/50mv:

victron energy smartshunt 500va/50mv

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. This SmartShunt now comes in a IP65 rated (Water resistant) option. Click here for product information.

The SmartShunt is a good alternative for a BMV battery monitor, especially for systems where battery monitoring is needed but less wiring and clutter is wanted.

Differences compared to BMV-712 Battery Monitor:

  • - No programmable visual and audible alarm.
  • - No programmable relay