but only after the battery has rested for 3 hours. The manufacturer provides us a battery’s voltage based on its state of charge. Remember, battery voltage levels are a moving target.

The above image shows a battery consistently drawn to 80% depth of discharge has a lifespan of about 600 cycles, compared to 1,600 cycles when drawn to 25% DOD.Ī battery’s remaining capacity (state of charge) is theoretically shown by its voltage. (From documentation for the VMAX AGM batteries).ĭrawing your battery to a low depth of discharge drastically reduces it’s lifespan. Obviously, you want to know how close the battery is to being dead. If there’s anything you take from this post – you need to have a method to reliably check your battery’s remaining capacity (state of charge). If the battery gets drawn too low, it can severely reduce its lifespan. We recommend reading this in-depth article on improving a battery monitor’s accuracy: The expertise to program the battery monitor to adjust for these variables is why we pay for them! Of course, battery monitor manufacturers understand these issues. This is like your car trying to tell you miles-per-gallon without knowing how fast you were driving. Battery voltage is a moving target.īattery monitors also display usage statistics (Amp-hours consumed). Battery voltage can go up or down just because it got colder or hotter.

It’s nearly impossible to total the number of Amps being absorbed when you don’t know how efficiently they are being absorbedĪ battery monitor’s state of charge computation is like a gas gauge – but imagine the level of gas in the tank (battery voltage) is always fluctuating.

A battery’s voltage varies significantly due to temperature, size, discharge rate, age, how recently it was discharged, etc.

Batteries lose capacity over time which the battery monitor cannot accurately account for.

The battery monitor works by using voltage and current entering and leaving the battery. But, battery monitors are pretty close and are (way) better than nothing.Ī battery monitor is often compared to the gas gauge in your car, but that is not a good analogy. In short, their figures are inaccurate due to variability in how batteries function. The thing is, battery monitoring is not an exact science.

i.e., if solar panels are generating +10A of current, and you are consuming (-6A) of current, the monitor displays positive 4A of current. The battery monitor shows us the “net” Amp current at any time. The shunt’s small data wire provides that data to the monitor display screen. The shunt is typically wired to the positive and negative terminals on the battery. We’ve got the higher end Victron BMV700.Īll current in or out of the battery goes through the shunt and gets measured. Alas, when we designed our solar system this product wasn’t on the market. If you’re going to be running any devices that potentially draw more than 1,000 watts, go for AiLi’s 350A version. But if the shunt ever fails, you’ll have to rewire things because you can draw from your batteries. If nothing breaks and you can deal with these issues, you’ll be pretty stoked to pay so little. Super short 2′ ft cable means you have to splice on additional cable to put the monitor display more than 2′ ft from the batteries.Hole for mounting is non-standard an unusual 2-1/8″ hole saw.The shunt housing is plastic which can crack when torquing the connections Bad instructions, and no technical specs.Display backlight stays lit whenever current going in or out, which can be hours at a time.

It’s pretty lacking on all other fronts though. It gives us the basics: the battery’s state of charge (it’s remaining power), and how many amps are going in or out of the batteries. The AiLi battery monitor is the kind of knock-off we are all familiar with: basically functional, but suspiciously cheap.

We will also give you our favorite battery monitors for different budgets. In this post we will review what a battery monitor does, whether you need one, and details to look for when comparing battery monitors. It’s also very likely to extend the life of your batteries. A battery monitor, especially a good one, makes using your battery power easier to understand and track. Not in the way that you need solar panels and cabling. Things to Look for in a Battery Monitor.Favorite High-End Battery Monitor (we’ve got this one):.Cheap Battery Monitor that will work and is better than nothing:.Our Recommendation for basically every electrical system:.Best Battery Monitors for Van and RV Solar System.

Rv battery system monitor