What is a Battery Monitor?
People often think of battery monitors as the fuel gauge of a battery. However, they do much more than just provide the state of charge of your battery system. Battery monitors also collect and display helpful data such as battery voltage, power consumption, estimated remaining runtime, current consumption, battery temperature, and more.
How a Battery Monitor Works
There are two types of battery monitors, shunt-based and voltage-based. The most simple type is the voltage-based monitor and frequently comes standard on most mobile power applications. This type of monitor just measures the real-time voltage of the battery and uses it to estimate its state of charge.
Voltage-based monitors are not very accurate because the real-time voltage of a battery will fluctuate based on temperature changes and other environmental conditions. If you change the battery type the voltage meter may even be completely inaccurate altogether.
The shunt-type monitor is much more accurate because it measures the actual energy flowing into and out of the battery. These battery monitors require a shunt to be installed on the negative side of the battery terminal. The shunt measures the real-time voltage of your battery system as well as the current draw.
The battery monitor uses these measurements to calculate the state of charge, power consumption, estimated remaining runtime, and other beneficial information about your battery system.
Battery Monitor Vs. Battery Management System (BMS)
Lithium batteries have an integrated battery management system (BMS) that helps optimize their performance and protect them from operating outside of safe conditions. The BMS is the control centre for individual batteries in a system, not the system as a whole.
The main function of the BMS is to prevent overcharging and over-discharging, which can damage a battery and shorten its life. The BMS also calculates the remaining charge, watches the battery’s temperature, keeps an eye on the battery’s health and safety by checking for loose connections and internal shorts, and balances the charge across all of the cells in the battery.
If unsafe conditions are detected, the BMS shuts the battery down to protect the lithium-ion cells and the user.
A BMS collects a lot of the same information as a battery monitor. However, instead of displaying the information to the user, the BMS uses it to optimize the performance and health of each battery.
Why You Need a Battery Monitor
The BMS collects data and uses it to optimize each individual battery. On the other hand, your battery monitor collects information and displays it so that you can know optimize the performance of your entire battery system.
One of the most basic functions of a battery monitor is to display the remaining charge of your battery system.
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. For example, your lights may dim as the batteries get low.
Conversely, lithium batteries do not experience a significant voltage drop as they drain. Without a battery monitor, there is no warning your batteries are dying until they are dead and the BMS shuts them off.
Helps You Take Better Care of Your Batteries
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.
A good example is deciding when to switch the fridge in your RV from battery power to propane. Perhaps it’s early evening, and your battery monitor says you have four hours of runtime left. However, if you switch your RV fridge to propane, you can make it through the night without needing to run your generator.
If using lead-acid batteries they should not be drained past 50 percent state of charge for optimum longevity. Using an accurate shunt-based monitor will let you know when you are reaching the 50% mark and that they will need to be charged. Lead-acid batteries also take a long time to charge and need to make it through an absorption cycle. Without a battery monitor you may not know when your batteries reach full charge. If they don’t make it to a full charge before draining you will shorten their lifespan.
Switching to lithium solves all these problems, but the battery monitor is still critical to know how much energy you have left, or how much you have charged the batteries.