If lithium polymer batteries (LiPo) used in drones are not used for a long time, self-discharge can cause the voltage of a single cell to drop below 3.0V, entering a state commonly referred to as "dormant" or "over-discharge." In this situation, ordinary chargers often interpret this as an abnormal voltage and refuse to start charging. To resolve this, you can use a "small current, slow charging" method to gradually bring the voltage back to the normal range before resuming normal charging. However, the entire process must be handled with extreme caution, strictly adhering to safety regulations.
Below are the specific operating steps and precautions:
I. Activation Strategy After Over-Discharge of LiPo Batteries
When a LiPo battery's voltage drops below 3.0V due to over-discharge, most smart chargers will trigger low-voltage protection, directly reporting an error or refusing to charge. At this time, you should not force-feed with a large current. Instead, you should use a small current to slowly "wake up" the cell, allowing the voltage to gradually rise back to the safe range before resuming normal charging.
Prerequisite Safety Conditions (Must Confirm)
Before attempting activation, you must first check the battery's appearance and condition:
If you find any abnormalities such as bulging, leakage, damaged casing, or unusual odor, do not attempt activation or charging. Treat it as a discarded battery and dispose of it according to safety regulations.
Only if the battery's appearance is intact and without obvious abnormalities can you continue with the following steps.
1. Measure Cell Voltage (This step is essential)
Use a multimeter or a charger with voltage detection function to check the cell voltage one by one through the balancing plug to confirm the current status:
If each cell voltage is ≥ 3.0V, you can directly use a 0.5C current for LiPo balancing charging.
If any cell is < 3.0V (especially below 2.5V), it needs to be "activated" first and cannot be charged directly using normal methods.
2. Low-Current Activation Procedure
Method 1: Using a Smart Charger with Repair/Activation Functions
Some smart chargers offer dedicated modes such as "LiPo Repair" and "Low-Voltage Activation," which can be performed as follows:
Set the charging current to approximately 0.1C–0.2C.
For example, for a 5000mAh battery, set it to 0.5A–1A.
Select the "Balanced Charging" mode, allowing each cell to simultaneously increase its voltage during charging.
The charging process lasts approximately 10–30 minutes. During this time, monitor the voltage changes to ensure it gradually rises above 3.0V.
Once all cell voltages have recovered to above 3.0V, stop the current mode and switch to regular balance charging (0.5C–1C current) to continue charging until fully charged.
Method 2: Manual Current-Limited Activation (Recommended for experienced users only)
If you don't have a charger with activation capabilities, you can use an adjustable constant current power supply for short-term activation, but this is riskier and requires extreme caution:
Set the output current of the constant current power supply to approximately 0.1C.
After connecting the battery, closely monitor the following:
Voltage changes
Abnormal battery temperature rise
Appearance abnormalities such as bulging or deformation
When the cell voltage slowly rises and reaches above 3.0V, immediately stop the constant current power supply activation.
Then, connect the battery to a standard LiPo balance charger and complete the subsequent charging using the normal balance charging mode.
The core principles of the above steps are: low current, slow recovery, strict monitoring, and immediate stop if any abnormality occurs. As long as the battery condition allows and the operation is performed safely, some over-discharged LiPo batteries that have entered a "dormant" state can be reactivated and restored to a usable voltage range.
II. Lithium Iron Phosphate (LiFePO4) Batteries: More Resistant to Over-Discharge, Reactivation Process Relatively Relaxed
The nominal voltage of a single LiFe battery cell is 3.2V, but after prolonged storage, the voltage may drop below 2.5V. However, compared to LiPo, LiFe has better over-discharge tolerance, therefore the requirements for recovery and activation are less stringent.
● Activation Steps:
Measure the voltage of each cell.
First, use a multimeter or a charger that supports cell-by-cell detection to check the voltage of each cell.
If a cell is below 2.8V, you can directly use a charger with a "LiFe mode,"
setting the charging current to a low current of 0.2C to 0.5C.
For example, for a 10000mAh battery, you can set it to 2A to 5A.
Activate directly using the standard LiFe charging mode.
No special "repair mode" or "activation mode" is needed:
Most LiFe-specific chargers are compatible with this type of lower voltage.
Charge continuously for about 30 minutes. Once the voltage of a single cell rises above 3.0V,
then increase the current to 1C and continue charging as normal.
Post-activation check:
After activation and full charge, perform a full charge test:
If the voltage of a single cell stabilizes at around 3.6V,
and the battery shows no bulging or abnormal deformation,
then the battery is in good condition and can continue to be used.
III. Nickel-Metal Hydride (NiMH) Batteries: Generally, no deliberate "activation" is needed; simple low-current charging is sufficient.
NiMH batteries are not very sensitive to over-discharge. Although the voltage will drop after prolonged storage, it rarely exhibits the "dormant" phenomenon seen in lithium batteries. Therefore, the recovery method is relatively simple:
Use a dedicated NiMH charger,
using a small current of 0.1C for trickle charging (e.g., 0.1A for a 1000mAh battery),
maintain this for about 1-2 hours to allow the voltage to gradually recover.
Then switch to the normal charging current of 0.5C-1C to fully charge the battery.
Furthermore, NiMH batteries do not have a significant memory effect; there is no need for deliberate "discharge and recharge" during daily use.
IV. General Safety Precautions for Activation Operations (Safety Always Comes First)
Before and after activating or low-voltage charging various batteries, the following safety points must be observed:
Never attempt to activate batteries that are bulging, leaking, have cracked casings, or are visibly deformed;
Do not leave the site unattended during activation or repair. It is recommended to operate in a well-ventilated, high-temperature resistant environment;
Use protective equipment such as fireproof bags, explosion-proof boxes, and metal trays to reduce the risk of accidents;
If the voltage does not rise significantly after multiple attempts, or if abnormal heating or odors occur during activation, immediately stop the operation and recycle the battery according to regulations. Do not continue to force its use.
Drone Equipment
So how do you determine if a drone battery has been successfully activated?
Essentially, it's about confirming that the battery voltage has returned to a safe range, can be normally recognized by the charger and continuously charged, and at the same time, minimizing the possibility of severely damaged battery cells. The following aspects can be considered when determining the success of a LiPo battery:
I. Core Standard: Single Cell Voltage Returns to a Safe Range
The purpose of activation is to restore the voltage of each cell to a range within which the charger can operate normally through low-voltage, low-current charging. Therefore:
1. Success Criteria for Lithium Polymer Batteries (LiPo):
When the voltage of a single cell rises to ≥ 3.0V, a standard LiPo charger can enter normal charging mode;
Ideally, each cell should reach above 3.3V for greater overall stability.
The key is that the cells should be basically balanced, with the voltage difference ideally controlled within ≤ 0.1V.
If any cell remains significantly below 3.0V, it is highly likely that it will subsequently relapse into "dormant" mode or experience capacity abnormalities.
2. Success Criteria for Lithium Iron Phosphate (LiFePO4) Batteries:
When the single-cell voltage recovers to approximately ≥ 2.5V, most LiFe chargers can begin charging normally.
After further charging, the single-cell voltage should reach above 3.0V, close to the normal storage voltage range.
3. Criteria for NiMH Batteries:
NiMH does not have a strict definition of "successful activation." As long as after low-current charging:
the single-cell voltage slowly climbs to ≥ 1.0V,
and can continue to accept the charging process,
the battery can be considered to have recovered from over-discharge or prolonged storage.
II. Key Verification: Can the Charger Successfully Enter Normal Charging Mode?
In actual operation, changes in the charger's status are the most direct indicator of successful activation:
● Changes in Charger Operating Status
Before Activation:
The charger may display "Low Voltage Protection," "ERROR," or show no response;
The indicator light may flash rapidly (e.g., a rapidly flashing red light);
The screen displays a current of 0A or "----", and charging cannot officially begin.
After Successful Activation:
The charger transitions to normal operating mode: The indicator light becomes steadily lit (e.g., a solid red light indicates charging, a green light indicates full charge);
The display shows a normal charging current reading, such as 0.5A, 1A, etc., instead of 0A or an abnormal symbol.
● Further Confirmation of Balancing Charging Mode (For Multi-cell Drone Batteries)
For drone battery packs with multiple cells connected in series, such as 3S and 4S, a further check is required using "balancing charging":
If the charger can correctly identify the voltage of each cell and smoothly enter the balancing charging process,
and simultaneously show that the voltage of each cell is gradually and relatively synchronously rising, then activation can be considered successful.
If only the total voltage of the battery pack recovers, but one or more cells remain low (e.g., still below 3.0V),
and the voltage difference is large, it indicates that the cell may be damaged. Even if the entire battery pack is "lit up," it cannot be considered truly fully activated and restored, and subsequent use carries a higher risk.
In summary:
Voltage meets standards + cells are balanced + charger works normally, indicating that the drone battery has been successfully activated.
If any of these conditions are not met, especially if there is a severe voltage imbalance or abnormal charging, the battery should be used with caution or scrapped immediately, prioritizing safety.
III. Auxiliary Judgment: Can the Battery Really "Store Electricity"?
After activation, it's crucial to confirm that the battery isn't just "pulling up the voltage," but truly storing electricity to avoid "false activation."
1. Observe After Fully Charging
First, charge with a small current of 0.1C to 0.5C (e.g., 0.2A to 1A for a 2000mAh battery) until fully charged:
LiPo: Single cell reaches 4.2V
LiFePO4: Single cell reaches 3.6V
After fully charging, unplug the charger and let it sit for 10 minutes. Then measure the voltage again:
If the voltage is relatively stable (LiPo single cell ≥4.1V, LiFePO4 single cell ≥3.5V), it indicates the battery has energy storage capacity;
If the voltage drops rapidly by more than 0.3V within 10 minutes, it's likely due to an internal short circuit or severe aging of the cell, indicating activation failure.
2. Light Load Discharge Test
If conditions permit, reinstall the battery in the drone and perform a 1-2 minute low-altitude short flight:
Observe whether the battery level drops normally and steadily;
Measure the voltage of each cell again after the flight:
If the voltage does not suddenly drop and the cells remain relatively balanced, the activation effect is reliable.
IV. Typical Situations for Activation Failure
The following situations generally indicate unsuccessful activation or battery damage, and the battery should be discontinued and scrapped:
Voltage hardly recovers: After 1-2 hours of activation, a single cell is still <3.0V (LiPo) or <2.5V (LiFePO4);
Abnormal heating: The casing temperature exceeds approximately 40℃ during the process, and it is noticeably hot to the touch, suggesting an internal short circuit;
Bulging or leakage: Bulging or leakage after activation, even if the appearance was normal before, indicates serious damage and poses a risk of fire or explosion;
Severe cell imbalance: After activation, one cell is >0.2V lower than other cells, and the difference continues to widen during charging.
V. Comprehensive Criteria for Successful Activation (Brief Version)
The following conditions generally indicate that the drone battery has been successfully activated:
Single cell voltage returns to a safe range:
LiPo ≥ 3.0V
LiFePO4 ≥ 2.5V
Charger functions normally: Enters normal charging mode with a stable charging current and no error messages;
Voltage remains stable after full charge without significant rapid drop;
Battery appearance is normal: No bulging, leakage, abnormal heating, and small voltage differences between cells.
It is important to emphasize that:
Batteries with severe over-discharge (e.g., LiPo single cell <2.0V), even if successfully activated, will experience a significant decrease in lifespan and reliability;
These types of batteries should only be used for low-altitude, short-duration flights, with enhanced voltage monitoring. Any abnormalities should be addressed by retiring the battery as soon as possible, prioritizing safety.
