A battery monitoring system functions like a fuel gauge for your RV’s battery bank. When RVing off-grid with solar it’s critical to have accurate data about the status of your battery bank such as:
- The State-Of-Charge (SOC) as a percentage available (e.g. 75% available)
- How much energy (in Amps and/or Watts) is being drawn from your battery
- How much energy is being replenished from your battery charger or from solar
- How much time remains before your battery runs out of charge
- Current Voltage of the battery bank
Without this basic information about your batteries you’ll just be guessing. So yes, you need a battery monitor that can track these things. Here’s what to look for.
First verify that it displays more than just battery voltage. It should include a device called a shunt. Without a shunt, it’s not possible to properly calculate the state-of-charge (or SOC).
With most battery monitors, the shunt is a separate device connected between the battery and the rest of the system. It measures all energy flowing in and out of the battery and passes that data back to the control/display unit.
How Battery Monitors Calculate the State-Of-Charge
Deep cycle batteries are rated in Amp Hours (Ah). So the battery monitor first needs to know how many Amp Hours of energy your battery bank can store when it’s fully charged.
Here’s an article explaining Amp Hours if you’re not sure what that means.
The shunt measures electrical current as it flows back and forth across it. Those measurements are sent in real-time back to the control unit. The control unit takes the current measurements over time and converts them into Amp Hours.
Finally, the computed Amp Hours are either added to or subtracted from the available battery capacity. Here’s how it works at a very basic level.
Electrical current (Amps) leaving the battery to power your gear is subtracted from the available battery capacity. Charge current coming back in from a battery charger or solar is ADDED to the available battery capacity.
EXAMPLE: A 100Ah battery charged to 100% has a 100Ah of available capacity. If you draw 10 Amps from your battery for one hour (10Ah), the SOC should read 90% (or 90Ah) remaining.
Now let’s put a 5 Amp charge back in your battery. After one hour 5Ah is added back to your remaining capacity. The battery monitor should now show a SOC of 95%.
Some systems may take it a step further with more sophisticated SOC algorithms, but all are based on measuring current flowing in and out of the battery bank.
My Top 5 Battery Monitoring Systems
All of the battery monitors listed will have the basic monitoring features previously mentioned. The models closer to the $200 mark may also include bonus features like these that you may want to consider:
- Remote Monitoring / Control via mobile App
- SOC Days/Hours Remaining
- Temperature Sensor
- Programmable Alarms and Alerts
- Triggered Relay (to activate equipment like generators or cooling fans)
- Integration and networking with other vendor equipment platforms (Victron)
- Firmware Upgrades with new features and bug-fixes
| Victron Smart Shunt | Victron Smart BMV-712 | Renogy 500A | AiLi 350A | DC 300A | |
 |  |  |  |  | |
| Max Current | 500A | 500A | 500A | 350A | 300A |
| SOC, Amps & Volts | Yes | Yes | Yes | Yes | Yes |
| Mobile App | Yes | Yes | No | No | No |
| Firmware Updates | Yes | Yes | No | No | No |
| Alarms & Alerts | Yes | Yes | Yes | No | No |
| Display Included? | No | Yes | Yes | Yes | Yes |
| Aux Battery Volts? | Yes | Yes | No | No | No |
| Price | $130 | $199 | $75 | $44 | $22 |
Victron Smart Shunt
The Victron Smart Shunt battery monitor is a compact module with the control unit and shunt combined. It is the successor to the popular Victron BMV-712 battery monitor used for 12V, 24V and 48V systems.
Unlike the BMV-712 though, the Victron Smart Shunt does not have a display unit. It communicates via wireless Bluetooth or through Victron’s VE.Direct cable interface.
You monitor and program the Smart Shunt using the Victron Connect mobile app or one of Victron’s GX devices (Cerbo GX or Color Control GX).
I like the versatility and compactness of the Victron Smart Shunt. It works seamlessly with other Victron equipment or as a stand-alone battery monitor.
Take a look at the Victron Smart BMV-712 instead if you prefer to have a mountable display. It has similar features.
The historical data logging is extremely useful. Use it to track battery SOC and energy usage over time. You can also monitor the voltage of a second battery and set up programmable alerts for low voltage.
Like all of the software controlled Victron equipment, you have the ability to update the firmware of the unit. Victron regularly updates its device firmware to add new features and keep the devices running properly for many years.
I use Smart Shunts in our off-grid systems. So it is my top pick.
Victron Smart BMV-712
The Smart BMV-712 has been a very popular battery monitoring system for many years. It shares all of the features of the Smart Shunt with the addition of a physical mountable display/control unit.
The shunt and display unit are separate physical devices. So you install the shunt near the battery, then mount the display unit inside your RV.
Finally, it’s a Victron Smart device. So Bluetooth capability is included for communicating with the Victron Connect mobile app and other Victron Bluetooth devices.
Renogy 500 Amp
The Renogy 500 Amp Battery Monitor includes a shunt and simple user-friendly display.
Renogy is known for providing battery and solar components at an affordable price. For around $75 this unit provides all of the critical battery information you’ll need to monitor a 12 volt battery bank including setting alarms.
The flush mountable display is clear and easy to understand and the 500A rated shunt matches the rating on the Victron monitors.
The Renogy 500 Amp battery monitor will get the job done, but expect the build quality and data accuracy to be a few notches below the higher-end units.
If you’re looking for a basic battery monitor to go along with your other Renogy equipment, then this may be a good fit.
AiLi 350 Amp
This is the no frills battery monitor similar to the Renogy 500 that displays essential battery status information on a fuel gauge style graphical display. The round flush-mount display is bright and basic.
For a budget battery monitor, it has received pretty good feedback from users. For the price, you can’t go wrong here.
DC 300 Amp
These very inexpensive battery monitors come in handy for lots of small applications. I’ve used them for testing batteries and other equipment, but several folks actually use them as their primary battery monitor.
For around $20 you get a shunt-enabled battery monitor that actually works. Changing settings on this unit is not user-friendly though, but it is doable. I’ve had some fail on me, but most were suitable for what I needed.
It’s actually amazing that there’s a viable battery monitor option at this price. It’s like buying cheap sunglasses. If you lose them or they break, no big deal. Just get another pair.