Calculation of battery charging among cellphone、tablet and Notebook

In theory, charging time = battery capacity/charging current. But there is something different in real.
The charging current is practically lower than charger’s current. For example, your tablet capacity is 4200mAh, and the charger’s output is 5v 2A. On the other hand, manual says 7h to full charge. And charging time is 4.2/2A=2.1h? That is real? Nope! Because the charging current is 4.2/7=0.6(lower than charging current).
However, 7h is just original time but changes longer and longer as time goes by. In most of the time, you may need charging 7.5h even longer in real.
Li-ion battery starts its protection to limit charging current when charging. Because when charging, energy leakage is unavoidable, resulting in unstable current transmission; excessive current will cause a load, which will increase the burden on the battery and risk of leakage. Most battery manufacturers have installed a protective board inside the battery to limit the transmission speed of the current and prevent dangers such as leakage. The batteries provided by batteryclub.org are equipped with protective plates to protect your device from being charged safely.