Power Battery Concepts and Principles

Power battery concepts, principles, the original can be so simple!

1. Voltage (V)

(1) Open circuit voltage: refers to the voltage of the battery when there is no external circuit or external load.

(2) Working voltage: refers to the potential difference between the positive and negative terminals of the battery in the working state that is, when the current flows through the circuit, also known as the load voltage.

(3) Discharge cut-off voltage: refers to the voltage reached when the battery is fully charged and discharged (if the battery continues to discharge, it is excessive discharge, which damages the life and performance of the battery).

(4) Charging limit voltage: charging process from constant current to constant voltage charging voltage.

                Battery charge-discharge voltage change curve

2. Battery capacity (Ah)

(1) Definition: battery capacity refers to the amount of electricity that the battery can store.

(2) Unit: capacity is expressed by C, and the unit is Ah (ampere hour) or mAh (milliampere hour).

(3) Formula: C=It, namely battery capacity (Ah) = current (A) x discharge time (h).

(4) Example: the capacity of 10 ampere-hour battery, 5 ampere-discharge can be released for 2 hours, 10 ampere-discharge can be released for 1 hour.

(5)Influencing factors: the actual capacity of the battery mainly depends on the following factors

(6) Rated capacity: the battery capacity measured under specified conditions and given by the manufacturer.

(7) Available capacity: under specified conditions, from the release of fully charged battery power.

(8) Theoretical capacity: assuming that the active substance is fully used, the capacity of the battery can be released.

3. Battery energy (Wh):

(1) Definition: refers to the amount of energy stored by the battery, expressed by Wh

(2)Formula: Energy (Wh) = rated voltage (V) × working current (A) × working time (h).

(3) Example: 3.2V15ah cell energy is 48Wh, 3.2V100Ah battery pack energy is 320Wh.

4. Energy density (Wh/Kg)

(1)Definition: refers to the energy released per unit volume or per unit mass, usually expressed by volume energy density (Wh/L) or mass energy density (Wh/kg).

(2) For example, if a lithium battery weighs 325g, has a rated voltage of 3.7V and a capacity of 10Ah, its energy density is 113Wh/kg.

                                                        The following table shows the theoretical value.

5. Power and power density

(1) Power refers to the energy output by the battery per unit time under a certain discharge system, and the unit is W or kW.

6. Discharge rate (A)

(1) Definition: discharge rate refers to the required current value when the rated capacity (C) is released in the specified time, which is equal to the multiple of the rated capacity of the battery in numerical value.

7. Charging method

(1) CC/CV: CC is constant current, with a fixed current to charge the battery; CV is a constant voltage, with a fixed voltage to charge the battery, charging current will gradually decrease as the battery is full.

(2) Trickle charge: the current is less than 0.1c to charge the battery. This is usually used when the battery is near a full turn and a supplementary charge is used at a turn. If the battery does not have strict requirements on the charging time, a trickle charge is recommended.

(3) Floating charging: at any time to charge the battery with constant voltage, so that it maintains a certain state of charge.

8, charge and discharge depth (SOC DOD) :

(1)State-of-charge (SOC) :

(2) discharge depth ofdischarge (DOD) :

(3) Deep discharge: indicates the extent to which 50% or more of the storage capacity is released.

9, Internal resistance (M ω)

(1) Definition: the internal resistance of the battery refers to the resistance caused by the current flowing through the battery when the battery is working.

10, self-discharge rate (% / month)

Results: the battery self-discharge will directly reduce the capacity of the battery, self-discharge rate directly affects the storage performance of the battery, the lower the self-discharge rate, the better the storage performance.

11. Cycle life (times)

(1) definition: the second battery after a charge and discharge is called a cycle or a cycle, the battery after repeated charge and discharge, the capacity will gradually decline, under certain discharge conditions, the battery capacity drops to 80%, the number of cycles the battery withstands is the cycle life.

(2) Influencing factors: improper use of battery, battery materials, electrolyte composition and concentration, charge and discharge rate, discharge depth (DOD%), temperature, production process and so on have an impact on the cycle life of the battery.