Why are battery monitors divided into voltmeters and coulomb meters?

As common solutions for displaying battery status, voltmeters and coulomb meters have fundamental differences in their measurement principles. This is also the core reason for their differences in accuracy and applicable scenarios.

Simply put, a voltmeter measures the voltage of the battery pack. Some voltmeters also display a percentage of remaining capacity, which is estimated based on the voltage curves of different battery types. Therefore, when using a voltmeter for the first time, you need to set the battery type, such as lead-acid, lithium ternary, or lithium iron phosphate, as well as the number of cells in series.

Voltmeters are easy to install and display information simply. Their biggest drawback is their lack of accuracy. Due to the internal resistance of the battery pack itself, voltage-based detection is often not precise enough. Moreover, many factors can cause the voltmeter reading to deviate from the actual value, such as significant voltage fluctuations when under load or charging, or increased internal resistance due to battery aging. Therefore, voltmeters are suitable for monitoring battery packs where high accuracy is not required and the battery is mostly in a static state.

On the other hand, a coulomb meter measures both the voltage and current of the battery pack. The displayed capacity, state of charge (SOC), power, and other parameters are calculated based on current, rather than estimated like a voltmeter. Current is not as easily affected by charging, discharging, or battery aging as voltage is, so coulomb meters are generally much more accurate than voltmeters. The disadvantages of coulomb meters are their higher cost and more complex installation. Aside from these factors, coulomb meters are the ideal choice for most battery monitoring scenarios.