Welcome to the EXPLORIST.life Mobile, Marine, and Off-Grid Electrical Academy!
Today, we are going to cover what a battery monitor is, where it goes, and why you need one. Clearing up confusion about battery monitoring and its purpose in your electrical system is exactly what we’re going to dive into in Lesson 1 of this Battery Monitoring series.
Understanding Battery Monitors – VIDEO
What Is the Purpose of a Battery Monitor
A battery monitor in your off-grid electrical system provides you with all of the vital information about your batteries. It tells you:
- How much power is remaining in your batteries
- How much time is left until the batteries are empty or full
- How many amps or watts are going into or out of your batteries (depending on whether they’re charging or discharging)
- The voltage levels of the batteries
Certain battery monitors, such as those from Victron, also offer historical data, including information like:
- The deepest discharge the batteries have undergone
- The number of charge cycles completed
- Other useful insights into battery health and performance
This data helps you understand the overall condition and efficiency of your battery system.
Is a Battery Monitor Necessary?
While a system can technically function without a battery monitor, operating without one would be like driving a truck without a fuel gauge or speedometer. Sure, the truck will still run—but you’d have no idea how much fuel is left or how fast you’re going.
A battery monitor provides essential feedback about your system’s “fuel” levels. While not absolutely required, it’s highly recommended for safely and efficiently managing your off-grid power system.
The Difference Between $10 and $100 Battery Monitors
There are two primary types of battery monitors:
- Voltage-Sensing Battery Monitors
- The older and simpler type.
- Connects directly to the battery to read voltage.
- Works well with lead-acid or AGM batteries because their voltage drops predictably as they discharge.
- Inexpensive—usually between $10 and $20.
- Shunt-Based Battery Monitors
- More accurate and more expensive ($100–$250).
- Use a shunt, which measures the actual current flowing into and out of the battery.
- Ideal for lithium batteries, whose voltage remains relatively flat even as they discharge, making voltage-only monitoring inaccurate.
Because lithium batteries don’t show much voltage change between 100% and 60% charge, shunt-based monitoring is the preferred and more reliable method.
State of Charge vs. Depth of Discharge
Battery monitors typically show two pieces of information:
- State of Charge (SOC): The percentage of the battery that is full (e.g., 100% = fully charged).
- Depth of Discharge (DOD): The percentage of the battery that has been used (e.g., 100% = completely discharged).
They are essentially opposites—if a battery has a 70% state of charge, it has a 30% depth of discharge. In practical use, most people refer to batteries by how full they are rather than how empty they are.
What Is a Shunt?
A shunt is the key component in shunt-based battery monitors. It’s a metal block with terminals on each end that measures the electrical current flowing between your battery and the rest of your system.
The shunt collects data about current and voltage, sends it to a small computer board, and then translates that information into useful metrics such as amps, watts, and battery percentage.
Common examples include:
- Victron SmartShunt
- Victron BMV-712
- Redarc Shunt
- Midnite Solar Shunt
Each uses similar principles, but may differ in features or display options.
How Is a Shunt Installed?
The shunt is wired in-line between the battery bank and the rest of the electrical system.
- The battery side connects to the battery’s negative terminal.
- The system side connects to everything else—loads, chargers, etc.
This setup allows the shunt to measure all current entering and leaving the battery bank, effectively acting as your system’s “fuel gauge.”
How Does a Shunt Display Data?
The way data is displayed depends on your specific setup.
- Bluetooth Connection:
Many modern shunts, like the Victron SmartShunt, transmit data via Bluetooth to the VictronConnect App, allowing you to view live battery stats from your phone within Bluetooth range (typically 10–50 feet).
- Connected Displays (e.g., Victron Cerbo GX or Ekrano GX):
These are more advanced monitoring hubs that can collect data from multiple devices in your system, including the shunt. When connected to Wi-Fi, you can even view your system data remotely.
It’s important to note that these hubs require a shunt (or batteries with built-in monitoring) to accurately read and display battery capacity.
Shunt vs. Batteries with Internal Monitoring
Some modern lithium batteries, like those from SOK and others, feature built-in monitoring systems. These can sometimes replace the need for an external shunt, but there are limitations:
- Internal monitors work well as standalone devices.
- Compatibility issues can occur when mixing brands (e.g., Victron systems with non-Victron batteries).
- A shunt is often a reliable fallback if firmware updates or communication protocols between brands don’t align perfectly.
For smaller systems, relying on internal monitoring may be fine. But for more advanced or integrated systems, including a shunt ensures reliable communication and data accuracy.
Wrapping Up
In this lesson, we learned what a battery monitor is, why it’s essential, and how shunt-based monitors provide more reliable data—especially for lithium batteries.
In the next lesson, we’ll take a closer look at several different battery models available from our store, shop.explorist.life, and demonstrate how they communicate with various apps and Victron equipment such as the Cerbo GX and Ekrano GX.
