Shunt Battery Monitor; are they worth it or not?
If you are looking at setting up a battery system, and want to know whether its worth fitting a Shunt Battery Monitor, this post covers our experience, and everything you need to know.
What is a Shunt Battery Monitor?
In essence, a Shunt Battery Monitor is a small electrical device that measures the electrical flow to, and from your battery, or batteries.
It will tell you things like battery voltage, real time power draw (or charge), time until empty (or charged), amp hours depleted from the battery, state of charge in percent and so on.
These are a calibrated piece of equipment that can tell exactly how much power is going to, and from your battery, and will give you an exact measurement of the state of charge of your battery, which is very hard to do with other methods.
As a practical example, we have a Victron Battery Monitor and Shunt in our Reconn R2 Hybrid Camper, and when we wake up often the two lithium batteries are sitting at around 70% state of charge, with 100 amp hours consumed from the battery and the battery volts sitting around 13.1
The freezer will likely be running, so it will show that there’s a 40W (or 3 amp hour load) on the battery, with 80 hours until the battery is flat (at the current rate of consumption).
If I turn the inverter and induction cooktop on, the current consumed is going to jump up to around 130 amps (around 1650W), and the battery voltage will drop to around 12.6 due to the draw, with the percentage dropping quickly and the amp hours consumed rising fast.
Once we’ve made breakfast, the solar will kick in, and after a couple of hours it will be doing 30 – 40 amps, replenishing our battery system.
By mid day, the batteries are usually full again, with zero amp hours consumed, voltage at 13.6 and indefinite power.
What is the advantages of a Shunt?
Trying to identify the condition of your battery without a shunt is extremely difficult.
With one glance (or by scrolling through depending on what battery monitor you have), you get the full picture of what your battery is doing, and then can make educated decisions with the information, or just walk away knowing its all happy.
If you are running solar, it can be almost impossible to know what is actually going on with your battery. We used to plug solar into a system without a shunt and you could see it was doing something (battery volts would go up), but you had no idea what it was doing, and how well it was performing.
With a shunt you know that its doing exactly 4 amps, or 2 if the fridge comes on, and it just all makes sense.
Trying to fault find a battery system when you have no idea what the batteries are doing is almost impossible.
What’s our experiences been with Shunt Battery Monitors?
My first dual battery setup on our 4WD just had a VSR, and a battery voltage gauge (actually the original one had nothing, so I had to use a multimeter!), and that’s what we used for many years.
Being lead acid batteries you could use the battery voltage (when resting) to get a reasonable idea of how charged the batteries were, and it worked just fine.
However, as we started to use heavier consuming appliances, this method became harder and harder, and when we finally moved over to lithium it is almost impossible to do as the discharge curve is so flat. Relying on voltage to tell how a lithium battery is sitting at is not reliable at all.
When we built our 230aH DIY lithium battery, I debated whether to just use the Bluetooth BMS as our ‘shunt’, and take readings from it.
However, I can tell you that these are very inaccurate compared to a proper shunt, and relying on them for anything more than a basic guide is a bad move.
Our camper trailer came with a Victron BMV 712, and it changed the way I thought about battery systems.
It made life so much easier to plan what needed to be done to keep a healthy battery system going, and after swapping to Renogy Lithium Batteries its been really helpful.
Our 230aH lithium in the Dmax is hooked to a Renogy battery monitor and Shunt, which I actually prefer as it displays all of the information on one screen, with no need to hop from one page to the next by pressing buttons.
I would never go back to an electrical system (unless it was very basic) without a shunt. The information you gain is just so much nicer to understand, work with and fault find as needed.
Are Shunt battery monitors worth it?
As mentioned above, we love our two shunt style battery monitors, and wouldn’t fit an electrical system without them.
They give you so much information, and ultimately peace of mind because at a glance you can tell everything is as it should be, and you can walk away knowing you won’t come back at the end of the day to a flat battery and a defrosting freezer!
When you can pick them up for under $150, its almost a no brainer.
Do you have a Shunt style battery monitor? What do you think of it?
