The FCC accuracy of a battery that is being deep cycled is about +/-5 percent compared to capacity readings taken by discharging. As the battery fades with usage and time, so also does the delivered energy decrease, and the FCC number will decline.
#Battery meter in car full#
The in-and-out-flowing coulombs can be used to estimate battery state-of-health known as full charge capacity (FCC). With each full charge, the battery resets the full-charge flag and during discharge, the coulomb counter measures the energy consumed. The SMBus battery stores the factory-set design capacity in Ah or 100 percent by default. Other than applying a controlled discharge, there is no reliable method to measure the capacity of “chemical battery” but there is a way to read the “digital battery.” The term chemical battery refers to the actual capacity derived by discharging a fully charged pack, whereas the digital battery is a peripheral monitoring circuit that stores the estimated capacity derived by coulomb counting when charging and discharging a battery as part of field use. Many users are unaware that the fuel gauge only shows SoC capacity, the leading health indicator, remains unknown. We ask, “100 percent of what?” If, for example, 100 percent of a good battery results in a 4-hour runtime, a battery holding half the capacity would run for only 2 hours. The fuel gauge resets to 100 percent with a full recharge regardless of how much capacity the battery can store.Ī serious breach of trust occurs if an aged battery shows 100 percent SoC while the battery’s ability to hold charge has dropped to 50 percent or less. While the SoC information displayed on a battery or a display screen is helpful to the user, the readout does not guarantee the runtime. Signal lights indicate the battery SoC when pressing the TEST button. Figure 1 shows a fuel gauge of a battery that is 75 percent charged with three lights glowing.įigure 1: State-of-charge readout of a “smart” battery On a partially discharged battery, half the lights illuminate, and on an empty battery all lights remain dark or a red light appears. When pressing the TEST button on a fully charged SMBus battery, all signal lights illuminate. A fuel gauge indicating state-of-charge fulfills this in part. One of the main tasks of the smart battery is to establish communication between the battery, charger and user. The battery continues to be a “black box” that conceals vital performance records and masks when the battery should be replaced.
The smart battery captures this capacity fade by reading the previous energy delivered, but these vital health statistics remain mostly hidden from the user. As the capacity fades, the runtime gets shorter. The lifespan of a battery cannot be defined by the number of cycles or age alone but to a large extent by its usage (or misusage).
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