Lithium-ion battery operating voltage
In lithium batteries used in consumer drones, the rated voltage of a single cell is 3.7V, derived from the average operating voltage. The actual voltage of a single lithium battery cell ranges from 2.75V to 4.2V, and the capacity marked on the lithium battery is the amount of electricity obtained by discharging from 4.2V to 2.75V. Lithium batteries must be used within this voltage range of 2.75V to 4.2V. If the voltage drops below 2.75V, it constitutes over-discharge, causing the lithium battery to expand and the internal chemical liquid to crystallize. These crystals may puncture the internal structural layers, causing a short circuit, or even reducing the lithium battery voltage to zero.
Lithium-ion battery charging voltage
A single-cell voltage exceeding 4.2V during charging indicates overcharging, resulting in an excessively vigorous internal chemical reaction. The lithium battery will swell and expand, and continued charging may lead to further expansion and combustion. Therefore, it is crucial to use a certified, safe charger to charge the battery. Unauthorized modifications to the charger are strictly prohibited and could have serious consequences! For safe flight, the single-cell alarm voltage can be set to 3.6V. If this voltage is reached or approached, the pilot must immediately initiate a return-to-home or landing maneuver, taking necessary safety precautions to prevent a crash due to insufficient battery voltage.
Lithium-ion battery discharge capacity
The discharge capacity of lithium-ion batteries is expressed in multiples (C), which means the maximum discharge current that the battery can achieve according to its nominal capacity. Common aerial photography batteries have C numbers of 15C, 20C, 25C, or higher. Simply put, 1C varies depending on the battery capacity. 1C means that the battery can operate continuously for 1 hour when discharged at a 1C discharge rate.
For example, if a 10000mAh battery works continuously for 1 hour, the average current is 10000mAh, or 10A. 10A is 1C for this battery. Another example: if a battery is labeled 10000mAh 25C, the maximum discharge current is 10A × 25 = 250A. If it's 15C, the maximum discharge current is 10A × 15 = 150A. This shows that during high-dynamic flight, a higher C-number allows the battery to supply more current to support the instantaneous power consumption, resulting in better discharge performance. Of course, a higher C-number also increases the battery price. It is crucial to never exceed the battery's discharge C-number, otherwise the battery may be damaged beyond repair or even explode.
Recommendations for the correct use of lithium-ion batteries in general power applications
There are six things to avoid when using batteries. Using them correctly is the best way to extend battery life.
However, let go
The battery discharge curve shows that the voltage drops rapidly at the beginning of discharge, but slows down between 3.9 and 3.7V. However, once it drops below 3.7V, the voltage drop rate accelerates, and improper control can lead to over-discharge, which can damage the battery or even cause the drone to crash due to excessively low voltage. Some modelers, due to having fewer batteries, over-discharge them every time they fly, resulting in very short battery life. The strategy is to fly for as little as possible, thus extending the battery life by one more cycle. It's better to buy two extra batteries than to fly them beyond their capacity limit every time. Make full use of the battery warning system; land as soon as the warning light comes on.
However, charging
There are requirements regarding chargers. Some chargers have inadequate power-off functions after full charge, causing a single battery to continue charging even when it reaches 4.2V. Additionally, some chargers, after a period of use, are prone to this problem of not stopping charging after full charge due to component aging. Therefore, lithium-polymer batteries must be supervised while charging. If the charging time is found to be excessive, the charger should be manually checked for malfunctions. If a malfunction is found, the battery should be removed immediately; otherwise, overcharging of the lithium-polymer battery can, at best, shorten its lifespan, and at worst, cause an explosion or fire. Furthermore, please remember to charge according to the battery's specified C-rate or a lower one, and never exceed the specified charging current.
Storage when not fully charged
A fully charged battery should not be stored at full charge for more than 3 days. If left uncharged for more than a week, some batteries will bulge, while others may not bulge immediately, but repeated full-charge storage may render them unusable. Therefore, the correct method is to charge the battery only after receiving a flight assignment. If there are no flight assignments within 3 days after use, charge each cell to 3.80~3.90V before storage. Even if the battery is fully charged but not used for any reason, discharge it to 3.80~3.90V within 3 days before storage. If the battery will not be used within three months, perform a charge-discharge cycle before storage to extend its lifespan. Batteries should be stored in a cool, dark environment. For long-term storage, it is best to place them in a sealed bag or a sealed explosion-proof box. The recommended ambient temperature is 10~25℃, and the environment should be dry and free of corrosive gases.
Without damaging the outer skin
The outer casing of a battery is a crucial structure preventing explosions, leaks, and fires. Damage to the aluminum-plastic casing of a lithium polymer battery can directly lead to a fire or explosion. Batteries should be handled with care, and cable ties should be tightened securely when securing them on an aircraft. During high-dynamic flight or a crash, the battery may be thrown out due to loose cable ties, easily causing damage to the battery casing.
Battery damaged casing
No short circuit
This situation often occurs during battery wire bonding maintenance and transportation. A short circuit can directly cause the battery to spark or even explode. When a broken wire is found in a battery after a period of use and needs to be re-bonded, special care must be taken to ensure that the soldering iron does not simultaneously contact the positive and negative terminals of the battery. Furthermore, during battery transportation, the best approach is to individually wrap each battery in a resealable bag and place it in an explosion-proof box to prevent short circuits caused by bumps and collisions during transport, which could result in the positive and negative terminals of a battery simultaneously coming into contact with other conductive materials.
Don't catch a cold
Many aviation enthusiasts overlook this principle. In northern or high-altitude regions, low temperatures are common. If batteries are left outdoors for extended periods, their discharge performance will be significantly reduced. Flying at the same timeframe as at room temperature will inevitably cause problems. In such cases, the alarm voltage should be increased (e.g., set the single-cell alarm voltage to 3.8V), because the voltage drop is very rapid in low temperatures; landing should begin immediately upon alarm activation. Furthermore, batteries should be insulated. Before takeoff, batteries should be stored in a warm environment, such as indoors, in a car, or in an insulated box. At takeoff, batteries should be installed quickly, and the flight mission executed. During low-temperature flights, the flight time should be reduced to half that at room temperature to ensure safe flight.
DJI Smart Battery Maintenance and Daily Use
DJI pioneered the Smart Battery System, significantly reducing the daily battery maintenance required by drone pilots. Although called a Smart Battery, the energy storage method and materials remain unchanged. Therefore, we cannot completely rely on Smart Batteries and neglect battery maintenance. DJI Smart Battery maintenance includes the following points:
Setting the automatic battery discharge time in DJIGo
Setting path: DJIGo---Enter the aircraft interface General Settings---Smart Battery Settings Advanced Settings You will see the following interface. I selected 5 days self-discharge, but you can freely set it from 1 to 10 days according to your flight frequency.
Label each battery
For drone pilots with multiple batteries, numbering the batteries is very important, even though smart batteries don't require checking the battery level on the drone. Numbering them makes it easier to manage multiple batteries; I simply number them according to the order I purchased them.
Battery storage
Smart batteries release heat during self-discharge, and although lithium-ion batteries are now very mature, there is still a chance of spontaneous combustion. In dry air, I usually place the battery in a well-ventilated place away from direct sunlight and flammable materials (to prevent spontaneous combustion from causing greater damage).
Storage requirements:
Storage temperature: -20°C to 45°C for storage periods less than 3 months.
Storage time greater than 3 months: 22 to 28°C
Charging ambient temperature: 0 to 40°C
Battery charging and discharging
Smart batteries feature automatic power-off when fully charged and automatic discharge during storage, saving considerable hassle. However, since the battery material remains unchanged, manual full charge and discharge cycles are still required to calibrate the battery's charge level. It is recommended to perform a full charge and discharge cycle of 10-20 times, allowing the battery to cool down before fully charging it (remember not to completely discharge the battery and then leave it unused, as this will damage the battery cells). A fully charged battery at 80% after discharge can be stored for extended periods.
Daily usage precautions for smart batteries
Before each flight, check the battery level and try to take off with a full charge. Estimate the wind speed at your flight path before takeoff, as wind strength directly affects aircraft power. Stronger winds will cause the aircraft to generate additional power to counteract the wind, leading to faster battery consumption. High-G maneuvers, rapid ascents and descents, or extremely high speeds will all accelerate battery drain; don't blindly trust the battery's power indicator. When flying in high-altitude areas, near lakes, or in mountainous regions, plan your battery usage according to your flight route; relying solely on the battery's return-to-home indicator may be too late. Finally, I wish you all a smooth and safe flight!
