Top from left to right: The CruzPro VAH-30, the Trimetric 2020, the CruzPro VAH110. Bottom: the Link 10 and the Microlog.

Simply measuring the voltage of a battery in use is nearly worthless for giving the amount of charge left in a battery or bank of batteries. The only exception is when the battery is under no load, and it has been sitting for 30 minutes.

If you want a real time “gas gauge” for your battery, a battery monitor is the way to go. They predict how long the battery will last at a given load, and update—in real time—as you add or remove loads. These monitors have varying capabilities, from simply providing an accurate measurement of volts and amps, to amp-hours, battery capacity, percent of power remaining, and so on.…