For our first six months or so, when we boondocked, we played the guessing game with our battery levels.
Are we fully charged? What percentage are we at now? How much time is left till the lights go out? Will our furnace be able to run all night?
These are things you just don't have to think about in a house. But, the struggle is real in an RV!
Voltage
Measuring voltage is the default way to measure SoC (State of Charge) in most RVs. If you search google for “battery state of charge by voltage“, you can find all kinds of resources showing what voltage equates to what SoC for various battery types. This type of measurement can be somewhat accurate.
The issue is getting an accurate voltage measurement! And that's the real issue. There are so many things that will perturb the measurement. Charging will make the measurement high. Using the batteries will make the measurement low and batteries are always in use in an RV. The temperature and condition of the batteries can also throw off the measurement.
The only way to get an accurate measurement is to disconnect the batteries from the RV and get a measurement at the batteries. That's not a pain, right? And it's still not super accurate even if you do!
You can also use a hydrometer to measure the gravity of an electrolyte sample from you pull from the battery. But, that's even more unrealistic than unhooking them to get a voltage measurement!
The bottom line is, the voltage number you might see on the control panel in your RV is wildly inaccurate!
Shunted Battery Monitor
A shunted battery monitor has a huge advantage over voltage-only monitoring! That advantage is in its name, and it's the shunt!
The shunt sits between your battery bank's negative terminal and everything connected to it! This means it can “see” all current flowing into and out of the battery bank. Nothing goes in or out without being seen by the shunt!
Having the data provided by the shunt, a smart battery monitor like the BMV-712 can use that data to compensate for current going in or out and give you an accurate voltage measurement. Not only that, but it can also tell you exactly how many amp-hours have been used and a very precise SoC (percentage).
Given the known total amp-hours of your battery bank, how much has been used, and how much it being drawn (used) at any given time, it can also tell you how long your batteries will last!
This information is GOLD!
Victron BMV-712 Battery Monitor
After our typical deep research into the topic of shunted battery monitors, only one really stood out: the BMV-712 by Victron.
We've been using the BMV-712 for well over a year and IT IS AWESOME!
State of charge (percent), actual voltage, amp-hours used, amp-hours remaining, time remaining, everything you want to know about your batteries all at your fingertips in the control panel!
Additionally, it has Bluetooth connectivity to any smartphone via the Victron Connect App! See all of your battery bank's parameters in one screen. The app also enables you to set alarm levels for SoC, so you don't get caught by surprise!
We very highly recommend the BMV-712!
Installation
The installation of any shunted monitor will be about the same. It's not complicated in a technical sense. Simply install the shunt on the negative side of your battery bank and connect every negative connection to the shunt if they can fit. It there are too many connections, use a bus bar. Nothing should connect directly to the negative side of your battery bank except the shunt.
Connect the control cable and monitor and that's it for the most basic installation.
Of course, if you want to mount the monitor inside the RV, that opens up a whole other can of worms that you'll need to figure out.
Below is an image of our installation. You can see that I decided to move everything off the battery bank and use bus-blocks. I also installed a battery cutoff switch to the positive side.
Summary
Quit playing the voltage guessing game! Get a shunted battery monitor and be in control of your RV's battery bank!
Products in this video
➡️ Victron BMV-712 Battery Monitor: amzn.to/2T5CkMm…
➡️ Blue Sea Systems 600A Bus Bar: amzn.to/37NSLCk…
➡️ Inverter and Battery Gear: www.amazon.com…
➡️ Battle Born 100Ah Lithium-Ion Battery: changinglanesrv.com…
➡️ 4 X TROJAN BATTERY T-105 PLUS 6V: amzn.to/39W6N67…
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