So now that we’ll be traveling a lot more, we’re going to need an RV battery monitor to keep a closer eye on our battery levels. Over the last couple of years we’ve (mostly) had access to shore power, so draining our lead acid batteries was never an issue.
Looks like that’s going to change.
And there’s no sense in destroying a perfectly good battery by abusing it. So it was time for the installation!
What is an RV battery monitor?
A Battery monitor is a like fuel gauge for electric systems. They help you keep track of your RV’s battery state and charging status.
- An LED display screen can give you information like
- Charging amps
- Amps coming in
- Battery Voltage
- Battery Amp Hours
- Battery capacity
Why is monitoring your RV battery level important?
By monitoring your batteries, you can ensure that they are always in good condition and prevent them from becoming overcharged or undercharged. This can help extend the life of your batteries so you’re not shelling out big bucks to replace them.
For example, if you drain typical lead acid batteries to under 50% you can usually get 200 drain/charge cycles out of them before they need to be replaced. However, if you drain them to only 70%, you can typically get 700 cycles out of them. That’s a significant increase in life span!
Also, it can cause damage if you drain too low because it can cause irreversible sulfation of the battery’s lead plates. When a battery is discharged too deeply, sulfur crystals will form on the lead plates, preventing the battery from holding a charge and you may need to replace it altogether.
So, by installing and using an RV battery monitors, you can extend battery life and use that money to invest in one of thos fancy suspension camp chairs!
What Things Does a Battery Monitor Measure?
An RV battery monitoring device enables RVs to accurately display their charge and load on a battery. The system displays the cycle length as well as the battery history of the device. The battery’s monitor is equipped with shunting to measure the power that comes into the cell battery.
Using this tool, owners will have an accurate record of how much power remains on their batteries to take the necessary steps.
Challenges with Measuring a Battery’s Charge
A battery measurement system that only measures the voltage to show charge levels does not necessarily provide the best results. Since battery capacities change according to ambient conditions like usage and temperature, the inaccuracies can be significant.
So, systems that incorporate multiple variables are more accurate.
What to look for When Buying an RV Battery Monitor?
Accuracy
It’s probably an obvious point, but a pricier battery monitor tends to give a more accurate reading. If you have a significant investment in your battery bay, protecting it by knowing EXACTLY your battery’s state is vital.
Accurate battery monitor options are more expensive because they are engineered to consider multiple variables. For example, cheaper versions often determine battery capacity only through voltage drop. If a fully charged battery discharges 12.8 volts, when the voltage drops to 11.8 volts, the monitor calculates the remaining amp hours on the battery.
However, this is often not accurate. The temperature of the batteries, how much load on them, and other variables can impact how many amps you REALLY have left.
More accurate battery monitors also use shunts instead of voltage sensors. Shunts are extra hardware that all of the current passes through. Thus, they can accurately determine power consumption.
Battery Type
You need to match the battery monitor with your battery bank. While some monitors will work with both lead acid or lithium, for example, others are designed to work with only specific kinds of batteries.
How Many Watts?
Different monitors have different capacities. If you’re blasting 30000 watts through a shunt, it needs to be rated for that kind of power.
Be sure to complete a power audit of your RV so that you can choose the correct monitor.
Features
While accuracy is a major factor in choosing most battery monitors, you may also be interested in various features.
For example, some monitors have bluetooth capabilities. Using blue tooth, you can simply check your phone rather than having to look at the display unit.
A display unit itself can also boast features. Some have automatic sleep mode so that power usage drops. (Some are so bright they can double as a nightlight!)
Others store historical data so that you can see patterns of discharge rate. That way you can predict charge needs and know when you might need to connect the generator to provide power to the battery bank!
Installing a Battery Monitor
I chose the AILI RV battery monitor for our skoolie. I don’t have high end lithium batteries in my battery bay, so I didn’t feel the need to invest over $200 in something like a Victron BMV 712.
Even the Renogy Battery Monitor was around $70 and more than I felt I really needed to spend.
The AILI battery monitor has a shunt for accuracy and monitors all the information that I need: charging rate, battery capacity, the voltage being used, and probably even some other info that I don’t really need.
Unboxing
When I first got the monitor, I took everything out of the box to try and figure it all out.
Then I took it one step further and hooked everything up on the kitchen table. (Much easier deciphering everything there rather than in the cramped quarters of the battery bank!)
(Warning: the printed directions of the AILI RV battery monitor are microscopic! Unless you feast on carrots you’ll need a magnifying glass to read them. I looked up the online directions so that I could actually see them!)
First, I hooked up the negative side of the battery to the B- lug of the shunt. (I keep an older but functioning car battery kicking around just for projects like this!).
Since the shunt has a capacity of 2000 watts, the lugs are large! So I used 4 gauge wire to make the necessary battery cable. I crimped on the positive and negative terminals to the battery cable, then connected the negative cable to the P- side of the shunt.
To simulate a load, I brought out one of the old bus flashers. I connected the negative side of the bus flasher to the other side of the shunt.
I connected another wire that supplies power to the monitor to the positive battery lug and inserted the other end into the tiny green box on the shunt. You need really thin gauge wire…(like 20 gauge) or it won’t fit!
Then, to connect the display unit to the shunt you simply plug in the harness. (Pretty easy to install, actually!)
Once you connect the display unit to power and the shunt, it lights up, and you can see the voltage reading.
To see how a load impacted the data, I connected the positive terminal to the positive side of the flasher light.
Now I had a model electrical system! I could see the voltage drop just a bit on the display. And by toggling the buttons on the display I could switch back and forth from seeing voltage or amp draw.
Install on the Bus
Having set it up on the kitchen table made it a relatively simple project on the skoolie. (Except instead of sitting comforably close to the fridge I was crouched in the cramped quarters of the battery bank!)
I did have to drill a 2 1/8″ hole in the side of the storage bay closet to mount the display. (Which wasn’t hard, but because it was a 2 sided wall, the odds of me dropping the mounting bracket down into the wall were high. So I secured it with some fishing line just in case. Glad I did…)
I screwed the wing nut onto the mounting bracket to lock the display module in place.
Next, I plugged the cable from the display into the shunt.
Then connect the negative wire to the battery terminal and shunt, and connect the power wire to the positive battery terminal.
All my 12 volt negatives ground to the chassis of the bus (mostly through the ribs) so I ran a cable (that had previously connected to the negative side of the battery) from the B side of the shunt to the bus rib.
The mounting holes on the shunt are TINY! Even a trim screw couldn’t fit in there…so right now the shunt is secured only with wires!
(You’ll notice that most of my wiring is repurposed from the bus itself. To see how how removed the wire without disabling the bus, check out the post here.)
Programming the Display
When you first fire up the monitor, you need to program it accordingly.
By pushing and holding the button on the right, I accessed the battery amp hours capacity and entered 120.
Then, since the battery was fully charged, I pushed and held the button on the left for 3 seconds, and set the charged state to 100%.
Conclusion
Keeping an eye on battery status can save a fair amount of money by prolonging their life. The simple install of a system in your skoolie, RV, or camper van conversion doesn’t have to be expensive.
If you have a
FAQ’s
- How accurate are battery monitors?
Typically you get what you pay for. Pricier RV battery monitors utilize more technology and more hardware to take into account the multiple variables like battery voltage, temperature, and loads to better determine the current amp hours capacity.
Plus, you need to have installed and programmed the battery monitor optimally to maximize accuracy.
In short, a high-end, properly installed, and programmed battery monitor can be very accurate. The question becomes, is your electrical system THAT sensitive that it needs it?
In some cases, with an expensive battery bank, charge controller, solar panels, and sophisticated wizardry in the system, getting an accurate state of your RV batteries with a high-end battery monitor protects your investment.
If your RV batteries are a couple of Lead-Acid’s from Walmart, but they suit your needs fine, you don’t need the Victron BMV 712.
- How do I monitor my car battery?
- There are both marine and car battery monitors available. Some automotive monitoring systems simply plug into power ports. Marine monitoring systems tend to be more complex since many boats have both motor and “house” batteries.
- Do I need a battery monitor in RV?
No. I’ve gone two years without an RV battery monitor. But I’ve had regular access to shore power. If you plan on boondocking, a system to monitor batteries can significantly prolong their life.
- How do battery monitors work?
While there are subtle variations, battery monitors measure current and use algorithms to calculate how many amp hours have been used and how many more are left in the batteries.
- How do I monitor my RV battery level?
Install a battery monitor. 🙂
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