How To Monitor RV Batteries and Never Run Out of Juice!

rv battery
If you have any plans of traveling without hookups, or boon-docking, then a battery monitoring system (BMS) will be a crucial gadget in your rig.

Some RVs will not come with a BMS. Sounds strange, right? We agree, but that’s just how the cookie crumbles. Other models of RVs will come with a very basic BMS. The good news is that investing in a BMS is an easy, life saving step to complete.

To tell the story short, the life of your RV battery can be monitored via a BMS or battery monitoring system. Installing one will help to keep you informed about the longevity of your battery, where it’s at in its charge, and when to plug the sucker up for more juice.

Why is a Battery Monitoring System Important?

Have your lights ever cut out in the middle of eating dinner? Or have you reached your hand into the fridge only to find lukewarm food and beverages?

Well, these things happen to the best of us. Up until we invest in a battery monitoring system to ensure we never accidentally run out of battery power again. Because without a BMS, there’s no sure fire way of knowing the status of your battery.

How Does a BMS Work?

Renogy 500A Battery Monitor

A battery monitor system calculates the amount of energy running in and out of your batteries at all times. In battery jargon, a BMS measures the state of charge and depth of discharge.

The state of charge is the level of charge relative to the battery’s capacity. 0% is empty and 100% is full.

The inverse of that is the depth of discharge. This measurement represents the percentage of battery capacity that has been removed from the fully charged battery.

So, as the state of charge decreases, the depth of discharge increases. That was a mouthful.

If all that didn’t quite site right in your brain, just think of a BMS as a fuel gage for your battery. You wouldn’t want to drive your car without a functioning fuel gage, would you?

The Basics of a BMS

A battery monitoring system is comprised, more or less, of two important components: the battery shunt and the display monitor.

The battery shunt is the device that is in charge (pun intended) of measuring the energy flow in and out of your battery.

The shunt is installed next to the battery and connected directly to the negative battery terminal. That is how it is able to report measurements in real time.

The second important component is the display monitor. The monitors job is to display the information from the shunt in a helpful way.

The older, more basic monitoring systems will display this information digitally and numerically.  Newer battery monitoring systems can display the information graphically.

The Nitty Gritty

DC Multifunction Battery Monitor

Let’s get down to the nity gritty with regards to what our battery monitoring systems are actually doing.

For one, the BMS is measuring voltage. Keeping track of your voltage is one of the simplest ways to keep from damaging your batteries.

In general, batteries are fully charged at around 12.7 volts. At around 12.1 volts they are 50% charged. Having a rough idea of the voltage of your battery can shape your energy usage.

In doing so, you can avoid over-discharging your battery. Draining your battery all the way can do irreparable damage to the unit. So keeping track of voltage is crucial.

You will also know when your batteries are successfully being charged. Naturally, batteries will not hover at or above 12.7 volts. So if your monitor is showing that number whilst charging, you know the charging process is working well.

 A BMS will also measure amps. This can give you a good idea of how quickly your batteries are being used or charged. From there, you can estimate how long they will last based on your lifestyle and personal usage.

Measuring the amps can also be helpful for figuring out how much power individual devices are using. You can figure out which device sucks up the most juice, and how to avoid particularly “thirsty” combinations of gadgets- like waiting to turn the TV on after the microwave popcorn is finished.

And if you are relying on solar power, you can easily get an idea of how much sun your panels are getting and how well your panels are transferring that energy to your rig.

The Bells and Whistles

Victron BMV-712 Battery Monitor

Battery monitoring systems come at a variety of price points. Anywhere from $15 to $200. Depending on the the type of BMS you invest in, your system may or may not come with additional bells and whistles.

Some BMS packages will come with cables and fuses that need to be connected to the shunt in order to send information to the display monitor. They may also come with temperature sensors to monitor for overheating.

In this day and age, remote controlled battery monitoring systems are popular. The display monitor can be accessed via a mobile application on your phone that relies on Bluetooth or Wi-fi.

This type of BMS will also automatically update the software and firmware necessary to keep the system running smoothly.

And from what I understand, the operation of the Bluetooth applications on smartphones is really easy to use and extremely helpful.

For an example of one of these state of the art battery monitoring systems, follow, check out the video below.

What Else is a BMS Capable Of?

The BMS in your rig isn’t just capable of monitoring the battery life. A high quality BMS  can also tell you:

  • The exact amount of amps each piece of equipment is using
  • How much energy is going in or out of your battery in real time
  • What percentage of your total battery capacity is available
  • How much time is left before your battery is fully juiced up or drained

A Recap for Why You need a BMS:

  1. No more guessing when your battery is 100% charged. Figure out the true state of charge of your battery in real-time.
  2. Add longevity to your battery’s life by knowing when to charge and for how long.
  3. Understand the health of your battery by knowing measurements like the voltage, amps, and amp-hours.
  4. A BMS can help you plan for upgrades like solar power or a bigger battery bank.
  5. A BMS can help you trouble shoot when issues arise with your equipment.


Well, there you have it. The “why” and the “how” behind the reason we think every RVer should be traveling with a battery monitoring system.

No more power blackouts or sacrificing the usage of your favorite creature comforts in order to save power. The headaches you can avoid by knowing the status of your battery are totally worth shelling out a bit more cash for a decent BMS.

If the topic of RV batteries, watts, and amp-hours suits your fancy, then let us help you learn more by checking out this article about RV inverters and converters.



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