You can make many upgrades to your battery system, but one of the simplest and most useful is adding a battery monitor. Let’s take a look at what a battery monitor is and how it can help you get the most out of your battery system.
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.
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.
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 center for individual batteries in a system, not the system as a whole.Â
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.
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.
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.Â
Tip: Learn more about Charging Your LiFePO4 Batteries here.
All battery monitors should have the basic functionalities we covered above. However, we’ve found that the Victron BMV-700 series offers additional features and reliability that make it the best option available on the market today.
The BMV-700 series measures and tracks battery voltage, current, amp-hours consumed, and the state of charge. Additionally, it uses this information to determine an estimate of the remaining runtime you have available. These features are relatively standard in most battery monitors.
The BMV-700 also offers additional features that are less common in other battery monitors. The BMV-700 has programmable visual and audible alarms to warn you of irregularities in your system before they cause issues. You also have a programmable relay available that allows you to turn off non-critical loads as needed automatically. Some BMV-700 models also offer an additional input that you can use to monitor a second battery, monitor temperature, or midpoint voltage.
One of our favorite features of the BMV-700 is the ability to connect to it over Bluetooth with your smartphone. Bluetooth is integrated into the BMV-712 and can be added to other BMV-700 models using the Bluetooth smart dongle. The VictronConnect App makes it easy for you to monitor all of your real-time and historical system information as well as change your system settings.Â
The more information you have on your battery system, the better decisions you can make to optimize its usage. If you’re looking to get the most out of your battery system, a battery monitor is a simple, inexpensive, and fantastic upgrade to consider.
We know that building or upgrading an electrical system can be overwhelming, so we’re here to help. Our Reno, Nevada-based sales and customer service team is standing by at (855) 292-2831 to take your questions!
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5 thoughts on “What is a Battery Monitor and Why Do You Need One?”
hooking up the victron 700 to a Battleborn 100Ahr, with solar only via a victron mppt charger. I’ve changed the efficiency and Peukert’s exponent as suggested. Can you recommend other changes to improve accuracy of the monitor?
Hi Jim! Thank you so much for reaching out, we are more than happy to help answer this question! Changing the battery capacity, the discharge floor option to 0%, and the charge voltage to 14.4 will be the best things to implement for your monitor.
Is the location of the battery monitor important relative to the actual battery bank? Mine are on a boat with about 15feet between battery and the monitor.
Thanks
The shunt itself should be very close to the batteries. The little communication cable that plugs into the back of the round gauge can be far away, mine came with a 50 foot cable. I swapped it for one that is about 6 feet long to make it look neater.
Aá´¡esome post.