I noticed at 0% the cells still have 3 volts each!! so it is actually not totally discharged
To correct the tracking error that occurs, a “smart battery” in use should be calibrated once every three months or after 40 partial discharge cycles. [See Battery Calibration: BU-603] This can be done by a deliberate discharge of the equipment or externally with a battery analyzer. A full discharge sets the discharge flag and the subsequent recharge establishes the charge flag.
A “smart” battery can be seen as consisting of two parts: the electrochemical battery and the digital battery. The electrochemical battery is known as the actual energy storage vessel and the digital battery is the circuitry that predicts state-of-charge (SoC) and monitors other information. The digital battery provides the readouts but the truth lies in the chemical battery. Figure 1 illustrates the typical drifting away of the digital battery from the electrochemical battery and how periodic calibration corrects the error. The values are assumed and accentuated. http://batteryuniversity.com/learn/article/how_to_calibrate_batteries
The SMBus has other limitations, and a major one is the inability to display capacity. This creates a false sense of security by assuming that a recharge will always deliver a full runtime. An older battery with only 50% capacity will give a 100% SoC indication in the same way as a new pack would. The SMBus cannot make the user aware of the shorter runtime when the capacity gets low.
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