How To Choose The Best RV Battery Monitor For 12v Electrical Systems
Do you like to boondock off the grid in your RV? If so, chances are good you’ve had a time or two where you had to worry about your RV house battery’s charge level.
For such a seemingly simple thing, not knowing how your battery is charging or discharging can be nerve-wracking.
If this sounds like something you’ve been dealing with, then you might want to think about installing a battery monitor into your RV.
Battery monitors are a great way to optimize the performance and maximize the lifespan of your RV’s house battery bank.
Though there are a few important details that go into the benefits of a battery monitor as well as how to choose the best battery monitor to meet your goals.
Read on to Learn the basics of RV battery monitors and what to consider in terms of voltage, current and size, as well as how to program it for the type of battery you have in your RV, or van.
What Is An RV Battery Monitor And How Does It Work?
An RV battery monitor, which is a special battery monitoring device that closely measures the current flowing into and out of your RV’s house battery banks.
It includes an automatic and very accurate shunt that helps prevent overcharging.
Some of the best battery monitors have alert systems that detect when the 12 Volt house batteries are nearing full charge or are depleting from use.
Without it, you would be left guessing how your battery is doing, which can potentially damage your RV’s house batteries by accidentally overcharging or undercharging them.
A lot of the best battery monitors will also have data collection and other special features that let you understand usage to help maximize your RV electrical systems performance.
Why You Need a RV Battery Monitor?
You don’t technically “Need” a battery monitor in your RV. Though it is very handy, and will greatly reduce the risk of accidentally overcharging or accidentally depleting your RV’s house battery bank.
Many of the best RV battery monitors can be set up with alerts or monitoring apps to let you know when the battery level is getting dangerously near 50%, which can also damage your RV’s 12 Volt house battery bank.
There are even a few RV battery monitors that come with basic analytics. The data they collect can help you optimize battery use and performance.
Types of Battery Monitors
There are a few differences to factor in when choosing which type of battery monitor is best for your RV’s off the grid electrical system.
This includes the ways that the device actively monitors your RV’s 12 Volt batteries.
As the name implies a voltmeter carefully monitors the voltage in an RV’s house battery bank.
One of the possible drawbacks with them is that they don’t tend to collect a lot of information beyond telling you what the battery’s current charge is.
You don’t get to do a lot of optimization, though you still will be able to tell when a battery is getting closed to overcharging or is nearly depleted to 50% or less of the maximum charge.
Ammeter Or Ampmeter
While the correct term is “Ammeter” a lot of people refer to this battery monitoring device as being an “Ampmeter.”
It’s designed to track the actual amperage being discharged from the batteries, and it needs to be installed inline with the negative terminal of the 12 Volt RV battery.
The power then passes through the battery monitor and provides you with multiple pieces of information that you can use to closely monitor or optimize battery performance.
This includes data such as amperage, and voltage, as well as the remaining amp-hours, along with the battery’s current charge level.
We’ve really grown to love Renogy’s products. They are well-designed, reliable, and affordable. The Renogy 500A Battery Monitor is no exception. This little screen lets you know exactly what’s going on in your power system for under 100. Add Renogy’s BT-1 Bluetooth adapter and you can view your power system’s status in real-time on your phone.
- Accurate within 1%
- High and Low capacity alarm functions
- Compatible with Lead Acid, AGM, Gel, LiFePO4, Lithium-ion, and Nickel-metal hybrid batteries
- Works with systems from 10V to 120V
- Customizable battery size and voltage shut-off
- Backlit display
- Weight: 2.6 oz
- Monitor Size: 3.9in x 2.4in x 0.7in
The Renogy better monitor comes with a shunt – a low-ohm resistor used to measure current. You install this shunt between the negative terminal of your battery and the negative side of your power system. Once the shunt is installed, a small wire is connected between the shunt and the battery monitor. As your power system’s current flows (both in and out) through this shunt, the display on the battery monitor shows you how much power is being consumed (going out of the batteries) vs how much power is being put back in your batteries through charging sources. At a quick glance, the Renogy battery monitor displays your net power consumption. For example, if you are generating 40 watts of power from a solar panel, but have 60 watts of lights on at the same time, you are using 20w of your battery’s capacity.
The battery monitor “monitors” your net power flow at all times and calculates your net power flow against your battery size. Using this internal calculation, the battery monitor also displays your current battery percentage. Basically, the Renogy Battery Monitor shows you your net power flow at any given moment AND keeps track to let you know the current level of your battery.
Why It’s Awesome
Knowing how much power you’re really using is important to ensure your batteries last. For example, if you have a 100 Amp Hour battery and use 50Ah of power per day, your system isn’t going to last through a 5-day RV trip. Knowing how much each electric device in your van, RV, or boat allows you to be informed in your decisions of what devices to use and for how long.
As an example, we recently installed a Renogy Battery Monitor in a 46ft sailboat. We were experiencing battery problems but struggled to diagnose the cause. With the Renogy Battery Monitor, we discovered that the LED strip lighting in the boat that we thought was energy efficient actually uses 5x more power than the simple overhead lights we’d been avoiding.
Battery Monitors like the Renogy Battery Monitor have been around for a long time, but they have traditionally been in the 200 – 300 range. At under 100, Renogy’s monitor lowers the barrier of entry to closely monitor smaller power systems and large systems alike.
Add the optional BT-1 Bluetooth adapter and you can see your real-time power usage right on your phone using Renogy’s DC Home app. Curious to know how much solar you’re currently generating? It’s just a short tap away.
Workarounds don’t work
I have tried to live without a battery monitor and tried to use a voltmeter as a substitute; this doesn’t work.
The only method that can work, only on flooded lead-acid batteries, is to measure the specific gravity of the electrolyte. This is accurate but is only done as a maintenance measurement. It is nothing you would do frequently.
How Electricity “Works”
Volts = Pressure = Potential to create work
Volts are like measuring the depth of the water behind a dam. The deeper the water, the higher the pressure. It is the same with voltage. Higher voltage means more pressure and more potential to create work. Pressure alone does not do anything, except sit there, until you have current.
Voltage (pressure) is only one measurement that affects performance.
Capacity = Volume
The measurement of volume, like water backed up behind a dam, is the starting point. The more volume the longer you can sustain work. Bigger battery banks have more volume and thus can sustain current for a longer period. Current, measured over time, is how to measure how much of the capacity has been used. This is the critical measurement. Subtract the energy consumed to determine the energy remaining.
Amperage = Current = Work in process
Amperage is the measurement of current flow, like water in a river — how much current is flowing. This is a very important measurement but still is not the whole story. You need to know the voltage, current, and capacity.
Volume, not pressure measures the ability to sustain work
Grand Lake, on the Colorado River, (in Colorado) is 389 feet deep and holds sixty-eight thousand acre-feet. = One hundred sixty-nine pounds-per-square-inch pressure at the bottom.
Lake Havasu, on the Colorado River, (in Arizona) is 90 feet deep and holds more than six hundred thousand acre-feet. = Thirty-nine pounds-per-square-inch pressure at the bottom.
To create sustained work you need both pressure and volume. In terms of the ability to create work, Lake Havasu has ten times the ability to create work than Grand Lake. Even though the pressure at the bottom of Grand Lake is more than four times greater. Lots of pressure does not equal the ability to create more work. Enough pressure, coupled with ample volume, creates the formula for sustained work. You would have to empty Grand lake down to 25% of its normal capacity to have lower pressure, (equal to Lake Havasu), and then it would soon run dry and have very little potential for sustained work.
True, as you remove water from Grand Lake, the pressure at the bottom will gradually change relating to the loss of water. The problem is that with electricity, especially with lithium batteries, the voltage doesn’t change until most of the discharge has already occurred.
Lake Mead has more depth than Grand Lake and forty-six times the volume of Lake Havasu and dwarfs these lakes in terms of ability to create work. This would be the best of all worlds, with lots of pressure and large volume to create lots of work.
How a battery monitor works
All RV solar installs include solar panels, wires, a charge controller, and a battery. Most solar installs lack an accurate method to determine how much volume has already been used. To measure this you need to record current and elapsed time. If you could see the energy, like sand in an hourglass, then you would know when you are about to run out.
A battery monitor is the missing critical part
A battery monitor isn’t on this list of standard components and it is the number one missed item. Any solar installation that does not include a battery monitor is incomplete. Any battery without a monitor may be full or nearly drained. How could you know?
A voltmeter is not a good substitute — not even a close substitute. A battery monitor will give you a precise measurement of the battery’s state of charge by measuring the “volume” consumed. Without a battery monitor, you are merely guessing. As in the above water example, the larger the capacity of your battery, the more you will be guessing if you only measure the voltage.
A battery monitor is critical regardless of which battery type you choose. In fact, the more you spend on your battery, the more you need a battery monitor. The bigger the battery the more you need a monitor.
A battery monitor is the only tool that can measure the state of charge. Nearly all RV solar installations are missing this critical component.
Voltmeters only make people feel good
Sometimes, you can tell something about the state of charge of a lead-acid battery by using a voltmeter. The only way to do this is to disconnect the battery from all charging and discharging for several hours and then measure the voltage. This will remove the surface charge. Who does this? It just isn’t practical. Voltmeters on systems while being used don’t give you even part of the story. Voltmeters read high during charging and read low during a discharge. Charge rapidly and voltmeters read very high. Discharge rapidly and voltmeters read very low.
Since lead-acid batteries suffer life-shortening damage if you ever remove more than fifty percent of their charge, a battery monitor is critical to measure how much of the capacity has been used. Voltmeters cannot accurately measure the capacity consumed.
Why Does My RV Need a Battery Monitor?
You’ve got a fuel gauge on your RV, and it gives you critical information about how much fuel is left in your fuel tank, and how far you can drive before you run out of gas, stranding yourself. As the gauge shows the fuel level getting low, that’s your signal to pull into a gas station to refuel.
An RV battery monitor gives you similar information about the condition of your battery bank. It tells you how much power is left before you’ll run out. importantly, perhaps, it tells you when your batteries are approaching a level so low that it could damage them (lead-acid batteries in particular), shortening their lifespan.
So, you need to know the state of charge of your batteries at all times – not only because you don’t want to run out of power, but also because monitoring current and charge levels helps you to maintain and preserve the life of your batteries.
Knowing the state of charge of your batteries at all times not only prevents you from running out of power but also helps to preserve the health of your batteries.
What Features Should I Look For In An RV Battery Monitor?
There are a number of features that are important to a high-quality RV battery monitor. Let’s take a look at those features one by one, after which we’ll mention a few monitors that provide all of the features we’re highlighting here.
Does the Monitor Provide All the Information You Need?
One of the most important features of a good RV battery monitor is that it provides critical battery system information. This would include such metrics as the amount of energy going into your batteries to charge them and the amount of energy being consumed at any given point in time. This information should be provided in Watts (power) and in Amps (current).
You’ll also want the monitor to tell you the percentage of total battery capacity remaining, in real-time, as well as how much time remains before your battery will be depleted (and, conversely, how much time remains before your battery is fully charged).
Many RV “battery monitors” that come installed by the manufacturer are specifically inaccurate in this arena, displaying simple LED lights showing battery charge in 25% or 33% increments (E, ¼, ½, ¾, F or E, ⅓, ⅔, F for example).
Is the Display Easy to Read and Use?
As with any type of monitor, you want an RV battery monitor to be easy to read and easy to understand. Some LED displays are notoriously difficult to read. A good display will allow you to glance at your battery monitor and see exactly what’s happening with your battery bank. This means the screen is easy to read in daylight or at night, and the information is presented in an easily understandable way.
A good display is easy to read in daylight or at night and offers critical information at a glance.
Does the Battery Monitor Come with a Shunt?
A shunt is a very important component of an RV battery monitor. A shunt, when connected to a negative battery cable, measures the energy flowing into and out of a battery and the information is sent back to the monitor where you’ll see the information on the screen in real-time.
All power going into and out of the battery bank needs to go through the shunt in order to provide accurate information about the state of your battery bank.
Essentially, what happens here is that measurements from the shunt are used by the monitor to determine how much power you’re consuming (power being removed from the battery bank) and how much the battery is charging (power going into the battery bank). This information allows the battery bank’s state of charge to be calculated, ultimately showing you the percentage of power remaining for your consumption.
Does the Monitor Offer Alerts and Event Triggers?
The reason we want the information provided by an RV battery monitor is so that we can take appropriate action when necessary. For this reason, it’s also good to have a battery monitor that sends alerts to notify you of certain critical battery status changes.
If you have a battery monitor that sends alerts to your phone, for example, you can be alerted to issues related to critical battery capacity levels approaching as well as voltage level, current draw, and even temperature values.
Event triggers are also a very important feature of a battery monitor because they can allow you to program your monitor to trigger a particular action if a certain event should occur. For example, you could program your RV battery monitor to turn on your generator if your battery level should hit 50%. You could also program it to turn the generator off once the batteries are charged sufficiently to a level you program into the battery monitor.
Clearly, alerts and triggers are important features of a good RV battery monitor, especially because you’re not always inside your rig to monitor the status of your RV battery bank.
A good RV battery monitor will offer the ability to program alerts and triggers for certain events. For example, your battery monitor can trigger your generator to start up if your battery bank reaches a pre-programmed level.
Is the Firmware of the Monitor Upgradable for Longevity?
An RV battery monitor comes with software embedded into the system that essentially sends instructions to the system. Software that is embedded into hardware like this is called firmware.
From time to time, the manufacturer may need to update the firmware of your battery monitor system in accordance with changes in technology. When you’re shopping for a battery monitor, you’ll want to make sure the firmware is upgradable (via Wi-Fi or Bluetooth) so that you can take advantage of technology upgrades without having to buy a new battery monitor.
What Are Some Popular RV Battery Monitors With These Features?
Following are five battery monitoring systems that check off all the criteria we’ve noted above. The ability for these systems to provide all of these features reliably is surely the reason they’re five of the most popular RV battery monitors on the market.
In a future post, we’ll go into more detail on the features of each one.
All five of these battery monitors will provide everything you need to gauge the status and health of your battery bank/electrical system, and much more.
An RV Battery Monitor is an Important Component of an RV Electrical System
Regardless of the type of battery monitor you may be interested in using, a high-quality RV battery monitor is a very important part of your RV’s electrical system. Without it, you have no accurate gauge of the condition of your battery bank.
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