Comprehensive Analysis of Drone Battery Depth of Discharge (DOD)

Drone Battery

ENOV High-Energy drone batteries power industrial and commercial drones. Delivering 220–320 Wh/kg energy density, they enable long flight times (30+ mins) and support fast charging (2C). Perfect for aerial photography, surveillance, and delivery drones.

1. Core Definition of Depth of Discharge (DOD)

Depth of Discharge (DOD) refers to the percentage of a battery’s rated capacity that has been discharged during one charge-discharge cycle of a drone battery. It is a key indicator for measuring the “degree of use” of the battery and also one of the core factors affecting the battery’s cycle life.

The concept corresponding to DOD is State of Charge (SOC), and the two are complementary, i.e., SOC = 100% – DOD. For example, when the battery’s DOD is 30%, its SOC is 70%, which means the battery still has 70% of its power remaining.

The “rated capacity” here refers to the total amount of electricity that a battery can release when discharged from a fully charged state to the cut-off voltage under standard conditions (specific temperature and discharge current). Its unit is usually mAh (milliampere-hour), which is an important benchmark for calculating DOD.

2. Relationship Between DOD and Drone Battery Life

(1) Differences in Cycle Life Corresponding to Different DOD Levels

For lithium-ion batteries commonly used in drones, their cycle life has a significant negative correlation with DOD. The lower the DOD (the shallower the discharge), the longer the cycle life; the higher the DOD (the deeper the discharge), the shorter the cycle life. The specific data are as follows:

10% DOD (shallow discharge): At this point, the remaining battery power is approximately 90%, and the number of cycles is around 8,000-10,000, which corresponds to the state with the longest cycle life.

20% DOD (shallow discharge): The remaining power is 80%, and the number of cycles is about 3000 – 5000, which is shorter than that at 10% DOD.

50% DOD (moderate discharge): The remaining power is 50%, and the number of cycles is about 1000 – 1500, with the life further decreasing.

80% DOD (deep discharge): The remaining power is 20%, and the number of cycles is about 500 – 800, which already falls into the category of deep discharge, and the life is greatly shortened.

100% DOD (full discharge): The remaining power is 0%, and the number of cycles is only about 300 – 500. Moreover, the risk of using the battery increases significantly, making this method not recommended.

(2) Principle of How DOD Affects Battery Life

Deep discharge is likely to cause damage to the electrode structure. When the battery is deeply discharged, the copper current collector of the negative electrode is prone to dissolution under the over-discharge state. During recharging, copper dendrites will precipitate. These copper dendrites may pierce the diaphragm inside the battery, causing an internal short circuit, and in severe cases, even leading to thermal runaway. At the same time, deep discharge will also cause excessive delithiation of the positive electrode lattice, resulting in cracking of positive electrode particles and falling off of active materials, which directly leads to a sharp drop in battery capacity.

Deep discharge intensifies internal battery losses. After deep discharge, the internal resistance of the battery will increase significantly. During recharging, the polarization phenomenon of the battery intensifies, and the temperature rises accordingly. This will accelerate the side reactions inside the battery, further depleting the battery’s performance and shortening its service life.

3. DOD Application Strategies for Different Drone Scenarios

For different operation scenarios of drones, it is necessary to set the recommended maximum DOD and the corresponding landing alarm voltage (taking a 12S battery as an example) by combining the operation intensity, endurance requirements, and battery life balance. The details are as follows:

(1) Consumer Aerial Photography Scenario

Recommended maximum DOD: 70%

Landing alarm voltage: 3.55V per cell (total voltage is approximately 42.6V)

Application description: Consumer aerial photography has high requirements for battery life and flight safety. Reserving 30% of the power for return flight can not only meet the needs of conventional aerial photography but also effectively protect the battery and extend its service life.

(2) Plant Protection/Inspection Scenario

Recommended maximum DOD: 75%

Landing alarm voltage: 3.50V per cell (total voltage is approximately 42.0V)

Application description: Plant protection and inspection operations are characterized by high intensity and relatively long operation times. However, the continuity of operations can usually be ensured by replacing batteries. Therefore, appropriately increasing the DOD to 75% can meet operational needs while maintaining a balance in battery life.

(3) Logistics/Long-Endurance Scenario

Recommended maximum DOD: 80%

Landing alarm voltage: 3.45V per cell (total voltage is approximately 41.4V)

Application description: Logistics, transportation, and long-endurance flights have extremely high requirements for endurance, making it necessary to maximize battery power utilization. Therefore, it is allowed to increase the DOD to 80%. However, it is worth noting that the number of battery cycles will decrease by 30% at this time, and users should be well-prepared for the resulting changes in battery consumption.

(4) Racing/FPV Scenario

Recommended maximum DOD: 85%

Landing alarm voltage: 3.30V per cell (total voltage is approximately 39.6V)

Application description: Racing and FPV flights require extreme performance, demanding high speeds and power. They belong to scenarios where “performance is exchanged for life”. Therefore, the DOD is set relatively high. However, long-term and high-frequency use will significantly shorten the battery life, so it is necessary to check the battery status regularly.

I’d like to point out that the above alarm voltages are all values when the battery is under load. When the drone lands and the battery is in a fully discharged static state, the voltage will rise by 0.1-0.2V. In actual use, it is necessary to avoid misjudging the remaining battery power due to voltage rise.

4. Real-time DOD Estimation Method for Drone Batteries

To accurately grasp the real-time DOD of the battery during the flight of the drone, the calculation can be carried out through the following steps:

Please make sure to record the fully charged capacity of the battery: Before the drone takes off, confirm the rated fully charged capacity of the battery, denoted as Q (unit: mAh). This data can be obtained from the battery’s factory mark or the Battery Management System (BMS).

Calculate the discharged capacity during flight: During the flight, record the discharge current of the battery through the drone’s Battery Management System or related monitoring equipment, and perform an integral calculation on the discharge current to obtain the amount of electricity discharged during the flight, denoted as Q_discharged (unit: mAh).

Calculate the real-time DOD: According to the formula “DOD = (Q_discharged ÷ Q) × 100%”, the real-time depth of discharge of the battery can be calculated.

For example, if the fully charged capacity Q of a drone battery is 5000mAh, and the discharged electricity Q_discharged during flight is 3500mAh, substituting into the formula gives: DOD = (3500 ÷ 5000) × 100% = 70%. At this time, it is necessary to control the drone to return to the flight according to the requirements of the consumer aerial photography scenario.

5. Iron Rules for DOD Management to Extend Drone Battery Life

To maximize the service life of drone batteries, it is necessary to follow the “two don’ts and one do” DOD management principles:

• Don’t discharge to empty: Each time the drone lands, ensure that the remaining battery power (SOC) is above 20%, that is, the DOD does not exceed 80%, to avoid structural damage and performance loss of the battery caused by deep discharge.

• Don’t store the battery at full charge for an extended period: Long-term storage of the battery at full charge will accelerate capacity degradation. Data show that storing the battery at full charge for 7 days results in a capacity attenuation degree equivalent to completing one full charge-discharge cycle. Therefore, when the battery is not in use for an extended period, it should be stored with the power level maintained within the range of 40% to 60% (i.e., DOD in the range of 40% to 60%).

• Charge and discharge shallowly: During daily training or non-high-intensity operations, the charging upper limit can be set to 90% and the discharge lower limit to 30% through the Battery Management System, meaning the battery is cycled within the DOD range of 10% to 70%. By adopting this shallow charging and discharging method, the battery life can be doubled.

6. Core Summary

For every 10% reduction in the depth of discharge of a drone battery, its cycle life increases by approximately 1 time. In scenarios where drones have high-rate discharge and high battery value, controlling the DOD within 70% is the best balance point between battery use cost and service life. In actual operation, it is necessary to adjust the DOD in combination with specific operation scenarios flexibly, while also ensuring effective real-time DOD monitoring and daily life management, so that the drone battery can continuously and stably provide power for flight.