The essential definition of battery capacity
Battery capacity refers to the total amount of charge stored in the battery. The international standard unit is ampere-hour (Ah), which characterizes the ability of the battery to release charge under specific conditions. Its physical meaning is: 1Ah capacity means that the battery can discharge continuously for 1 hour at a current of 1 ampere. The actual energy output needs to be calculated in combination with the voltage platform, and the formula is electric energy (Wh) = capacity (Ah) × average working voltage (V). For example, a 5000mAh (5Ah) lithium battery releases 18.5Wh of electric energy at a 3.7V voltage platform, while a 5V battery with the same capacity outputs 25Wh - the voltage difference leads to different energy values.
The core principle of capacity measurement
The constant current discharge method is the basic measurement method: at a standard temperature (25±2℃), discharge at a constant current to a cut-off voltage (such as a lithium battery ≥3.0V), and calculate the result by the formula capacity (Ah) = discharge current (A) × duration (h). For example, a 1A current discharge for 4 hours results in a 4Ah capacity. It should be noted that in actual applications, discharge current fluctuations will lead to capacity deviations, so the nominal value is an approximation of ideal working conditions.
Equipment power demand calculation model
Determine the average daily power consumption: Statistical equipment operating power (W) and daily usage time (h), calculate daily power consumption Wh = W × h.
Calculate battery capacity: According to system voltage (V), solve according to capacity (Ah) = Wh / V.
Case: UAV motor power 200W, target endurance 0.5 hours, system voltage 22.2V (6S lithium battery pack):
Required power = 200W × 0.5h = 100Wh
Required capacity = 100Wh / 22.2V ≈ 4.5Ah (4500mAh)
Key correction factors affecting capacity
High rate discharge: The discharge capacity attenuation above 10C can reach 30%, and 20%-30% redundancy needs to be reserved during design.
Low temperature environment: At -10℃, the capacity of lithium battery drops to 40%-60% of normal temperature. Application in cold areas needs to be configured according to 1.5~2 times of demand.
Battery aging: After 200 cycles, the capacity decays by about 15%, and the available capacity needs to be dynamically converted according to the health level (SOH).
Three major technical misunderstandings of capacity cognition
Nominal capacity ≠ available capacity: The safe discharge range of lithium battery is usually 20%-90% SOC, and the effective capacity of a nominal 5000mAh battery is only about 3500mAh.
Discharge rate restricts output: The capacity of a 5C rate battery may decay by 50% when discharged at 10C. Special batteries with high rate requirements should be selected above 50C.
Energy density priority principle: The selection needs to compare the energy per unit weight (Wh/kg). The actual energy supply of ternary lithium (250Wh/kg) is better than that of lithium iron phosphate with the same ampere-hour (160Wh/kg).
Scientific charging and discharging strategies to extend life
Cycle depth optimization: Maintain the use of 30%-80% power range, and the life of deeper cycles (0-100%) is extended by 300%.
Temperature boundary control: The charging environment is strictly limited to 0℃-45℃, and the discharge environment is -20℃-60℃. Overtemperature will accelerate aging.
Rate management specifications: The ideal charging rate is 0.5C (such as 5000mAh battery charging with 2.5A), and the limit discharge does not exceed 80% of the nominal rate.
Empirical data: Following the above strategy can increase the cycle life of lithium batteries from 300 times to 800 times (capacity retention rate ≥80%). Application cases show that the capacity decay of DJI Mavic 3 battery in shallow charging and discharging mode is less than 5% after 200 cycles, which is significantly better than the deep cycle control group.
The essential definition of battery capacity
Battery capacity refers to the total amount of charge stored in the battery. The international standard unit is ampere-hour (Ah), which characterizes the ability of the battery to release charge under specific conditions. Its physical meaning is: 1Ah capacity means that the battery can discharge continuously for 1 hour at a current of 1 ampere. The actual energy output needs to be calculated in combination with the voltage platform, and the formula is electric energy (Wh) = capacity (Ah) × average working voltage (V). For example, a 5000mAh (5Ah) lithium battery releases 18.5Wh of electric energy at a 3.7V voltage platform, while a 5V battery with the same capacity outputs 25Wh - the voltage difference leads to different energy values.
The core principle of capacity measurement
The constant current discharge method is the basic measurement method: at a standard temperature (25±2℃), discharge at a constant current to a cut-off voltage (such as a lithium battery ≥3.0V), and calculate the result by the formula capacity (Ah) = discharge current (A) × duration (h). For example, a 1A current discharge for 4 hours results in a 4Ah capacity. It should be noted that in actual applications, discharge current fluctuations will lead to capacity deviations, so the nominal value is an approximation of ideal working conditions.
Equipment power demand calculation model
Determine the average daily power consumption: Statistical equipment operating power (W) and daily usage time (h), calculate daily power consumption Wh = W × h.
Calculate battery capacity: According to system voltage (V), solve according to capacity (Ah) = Wh / V.
Case: UAV motor power 200W, target endurance 0.5 hours, system voltage 22.2V (6S lithium battery pack):
Required power = 200W × 0.5h = 100Wh
Required capacity = 100Wh / 22.2V ≈ 4.5Ah (4500mAh)
Key correction factors affecting capacity
High rate discharge: The discharge capacity attenuation above 10C can reach 30%, and 20%-30% redundancy needs to be reserved during design.
Low temperature environment: At -10℃, the capacity of lithium battery drops to 40%-60% of normal temperature. Application in cold areas needs to be configured according to 1.5~2 times of demand.
Battery aging: After 200 cycles, the capacity decays by about 15%, and the available capacity needs to be dynamically converted according to the health level (SOH).
Three major technical misunderstandings of capacity cognition
Nominal capacity ≠ available capacity: The safe discharge range of lithium battery is usually 20%-90% SOC, and the effective capacity of a nominal 5000mAh battery is only about 3500mAh.
Discharge rate restricts output: The capacity of a 5C rate battery may decay by 50% when discharged at 10C. Special batteries with high rate requirements should be selected above 50C.
Energy density priority principle: The selection needs to compare the energy per unit weight (Wh/kg). The actual energy supply of ternary lithium (250Wh/kg) is better than that of lithium iron phosphate with the same ampere-hour (160Wh/kg).
Scientific charging and discharging strategies to extend life
Cycle depth optimization: Maintain the use of 30%-80% power range, and the life of deeper cycles (0-100%) is extended by 300%.
Temperature boundary control: The charging environment is strictly limited to 0℃-45℃, and the discharge environment is -20℃-60℃. Overtemperature will accelerate aging.
Rate management specifications: The ideal charging rate is 0.5C (such as 5000mAh battery charging with 2.5A), and the limit discharge does not exceed 80% of the nominal rate.
Empirical data: Following the above strategy can increase the cycle life of lithium batteries from 300 times to 800 times (capacity retention rate ≥80%). Application cases show that the capacity decay of DJI Mavic 3 battery in shallow charging and discharging mode is less than 5% after 200 cycles, which is significantly better than the deep cycle control group.
