# Explanation of terms for rechargeable battery

Capacity rate

(C-rate)

C is the first letter of Capacity, which expresses the rate of battery charging and discharging in terms of current

Formula: Charging efficiency = (discharging current * time from discharge to cut-off voltage) ÷ (charging current * charging time) * 100%

For example: when the rated capacity of the rechargeable battery is 1000mAh, it means that it takes 1 hour to charge with 1000mAh (1C). If it is charged at 200mA (0.2C), the charging time takes 5 hours, and the same is true for discharging.

Actual capacity

The capacity that can be released with discharge below 1C.

High rate capacity

The capacity that can be released by discharge above 1C.

Energy Density

The amount of energy stored in a unit of a certain space or mass matter. That is, the electric energy released by the average unit volume or mass of the battery. The energy density of a battery is generally divided into two dimensions: weight energy density and volume energy density.

The greater the energy density of the battery, the more electricity stored per unit volume or weight

Generally, in the same volume, 1.8 times of Ni-MH batteries and 2.5 times of Ni-Cd batteries are the energy density of Li-ion batteries. Therefore, when the battery capacity is equal, Li-ion batteries will be larger than Ni-Cd and Ni-MH batteries. Smaller and lighter.

End voltage

Refers to the minimum working voltage value allowed by the battery when the battery is discharged. If the voltage is lower than the discharge termination voltage and the discharge continues, the voltage at both ends of the battery will drop rapidly, forming a deep discharge.

The termination voltage of battery discharge will not all be the same, due to the different battery types and discharge conditions. According to regulations, the termination voltage must be inversely proportional to the discharge current, that is, the termination voltage will decrease if the discharge current increases.

Open circuit voltage

The terminal voltage in the energized state is called the open circuit voltage. The open circuit voltage of a battery is equal to the potential difference between the positive and negative electrodes of the battery when the battery is not energized (that is, when there is no current passing through the two poles).

The open circuit voltage of the battery will be different because of the material of the battery’s positive and negative electrodes and the electrolyte. If the materials of the battery’s positive and negative electrodes are the same, the open circuit voltage of the battery will not change regardless of the degree of change in the volume and geometric structure of the battery.