Battery Capacity
Battery capacity is divided into rated capacity and actual capacity.The rated capacity refers to the electric quantity that a battery should deliver when discharged at a 5‑hour rate to the cut‑off voltage at an ambient temperature of 20 ℃±5 ℃, denoted as C₅.The actual capacity is the real electric quantity released by the battery under given discharge conditions, mainly affected by discharge rate and temperature. Strictly speaking, charge‑discharge conditions shall be specified when stating battery capacity.
Capacity units: mAh, Ah (1 Ah = 1000 mAh).
Internal Resistance
Battery internal resistance is the resistance encountered by electric current when flowing through the battery during operation. It consists of ohmic resistance and polarization resistance.High internal resistance will reduce the discharge operating voltage and shorten discharge duration. Its magnitude is mainly affected by battery materials, manufacturing processes and cell structure. Internal resistance is a critical parameter for evaluating battery performance.
Voltage
Open‑circuit voltage (OCV) is the potential difference between the positive and negative electrodes when the battery is idle with no current passing through the circuit. Generally, the open‑circuit voltage of a fully charged lithium‑ion battery is about 4.1–4.2 V, and drops to approximately 3.0 V after discharge. The state of charge (SOC) of a battery can be judged by measuring its open‑circuit voltage.
Operating voltage, also known as terminal voltage, is the potential difference between the two electrodes when current flows through the circuit during battery operation. During discharge, the operating voltage is always lower than the open‑circuit voltage due to the resistance from internal impedance that current must overcome; the opposite occurs during charging. The typical discharge operating voltage of lithium‑ion batteries is around 3.6 V.
Discharge Plateau Duration
Discharge plateau duration refers to the discharge time from a fully charged state to a specified voltage.For example, to measure the 3.6 V discharge plateau duration of a ternary lithium‑ion battery: charge the battery at constant voltage to 4.2 V and stop charging when the charging current is less than 0.02 C (full charge), leave it standing for 10 minutes, then discharge it to 3.6 V at a given discharge rate. The elapsed time is the discharge plateau duration under that current.
Since electronic devices powered by lithium‑ion batteries have specific operating voltage requirements and will fail to work below the threshold, discharge plateau is one of the key criteria for assessing battery quality.
Charge‑Discharge Rate
Charge‑discharge rate is the current required for a battery to release its rated capacity within a specified time. Numerically, 1 C equals the rated capacity of the battery, usually represented by the letter C.For instance, if the nominal rated capacity of a battery is 10 Ah, 10 A corresponds to 1 C (1‑rate), 5 A to 0.5 C, and 100 A to 10 C, and so on.
Self‑Discharge Rate
Self‑discharge rate, also called charge retention capacity, indicates the ability of a battery to retain stored electric quantity under open‑circuit conditions. It is mainly influenced by manufacturing processes, materials and storage conditions, serving as an important performance parameter.
Efficiency
Charge efficiency measures how much electric energy consumed during charging is converted into chemical energy stored in the battery. It is mainly affected by battery manufacturing processes, formulas and ambient temperature. Generally, charge efficiency decreases as temperature rises.
Discharge efficiency is the ratio of the actual electric quantity discharged to the cut‑off voltage under specified discharge conditions to the battery's rated capacity. It is affected by discharge rate, ambient temperature and internal resistance. In general, discharge efficiency declines with higher discharge rates and lower temperatures.
Cycle Life
Battery cycle life refers to the number of charge‑discharge cycles a battery undergoes under a given charge‑discharge regime until its capacity drops to a specified value.According to Chinese national standard (GB) for lithium‑ion batteries, the capacity retention rate shall remain above 60% after 500 cycles at a 1 C rate.
