How to determine the lifespan of lithium battery electric bicycle batteries?
To determine the lifespan of lithium battery electric bicycle batteries, it is necessary to combine daily usage experience, data calculation and professional testing, and conduct a comprehensive analysis from three aspects: "intuitive performance - deep-seated causes - scientific verification". Specifically, it can be carried out from the following dimensions
I. "Life Warning Signals" in Daily Cycling: Seeing the Essence from the Surface
1. A "cliff-like decline" in driving range
This is the most direct manifestation of battery aging, with the core issue being the loss of active substances in the battery cells, which leads to a decline in power storage capacity.
The criterion for judgment: If the full charge range of a new battery is 50 kilometers and it drops below 30 kilometers (with a decline of over 40%), it indicates that the battery has entered its "middle and old age". If it drops below 20 kilometers (with a attenuation of over 60%), its lifespan is basically over.
Note to eliminate interference: Low temperatures in winter (below 0℃) can cause a temporary reduction in lithium battery capacity (possibly by 20% to 30%), and tests should be conducted in a normal temperature environment around 20℃. At the same time, check the tire pressure (insufficient tire pressure will increase resistance and reduce the range) and whether the brakes are stuck (extra power consumption), and ensure that the test conditions are consistent.
2. "Abnormal Changes" during charging
Battery aging can lead to a decline in charging and discharging efficiency, and abnormal fluctuations in charging time are important signals:
Fast charging and false charging: A battery that was originally fully charged in 8 hours suddenly shows "full charge" in 2 to 3 hours, but the battery level drops rapidly to below 30% during riding. This indicates that some cells have failed (such as internal short circuits or damaged separators), and the remaining cells are forced to "share" the charging amount, resulting in a "false full charge".
Slow charging and overheating: The charging time is more than 50% longer than that of a new device (for example, from 8 hours to over 12 hours), and the temperature of the battery casing exceeds 45℃ during charging. This may indicate an increase in the internal resistance of the battery cells (a typical feature of aging), a rise in the proportion of electrical energy converted into thermal energy, and a significant decrease in charging and discharging efficiency.
3. "Danger Signals" of Battery Physical State
Bulging and deformation: Even a slight bulge indicates irreversible damage inside the battery cell (such as gas produced by the decomposition of the electrolyte or micro-short circuits caused by lithium dendrites piercing the separator). At this point, not only does the battery capacity drop sharply, but there is also a risk of self-ignition, and it must be immediately shut down and replaced.
Abnormal heating: During normal charging and discharging, the battery temperature should be below 40℃ (warm to the touch but not scalding). If the casing becomes hot to the touch when climbing a slope or accelerating (exceeding 50℃), or continues to heat up during charging (exceeding 45℃), it indicates that the consistency of the battery cells has collapsed, and some cells are overloaded, which is a precursor to the end of their lifespan.
4. "Disordered fluctuations" in battery level display
The power decline of new batteries follows a linear pattern (for example, the riding distance between 100%-80% and 80%-60% is similar), while aged batteries will show:
"Power outage" : A sudden drop from 60% to 20%, or a direct power cut from 30%, indicates that some cells have completely failed, and the remaining cells cannot maintain a stable voltage.
"False high" : After a full charge, it shows 100%, but after riding for 5 minutes, it drops to 80%. In fact, it is due to excessive internal resistance of the battery, which cannot output a stable current and can only maintain a "surface voltage".
Ii. Data-driven calculation: Anchor the life cycle with "time + cycle"
1."Rough assessment by service life"
Ternary lithium batteries: Under normal use, the designed lifespan is 3 to 5 years. Even if the battery life is still acceptable after 5 years, the aging of the battery cells may increase the risk of thermal runaway.
Lithium iron phosphate batteries: They have a longer lifespan, typically ranging from 5 to 8 years. However, after 8 years, safety issues need to be closely monitored (such as bulging cells and failure of protection boards).
Note: If it is used for a long time in a high-temperature (> 40℃) or low-temperature (< -10℃) environment, or frequently overcharged or overdischarged, its lifespan may be shortened by 30% to 50%.
2. "Precise calculation" based on the number of charge and discharge cycles
Cycle definition: Charging from 20% of the battery to 80% counts as 0.6 cycles. Charging completely from 0 to 100% counts as one cycle (" shallow charging and shallow discharging "is more conducive to extending the lifespan).
Ternary lithium batteries: The cycle life is approximately 800 to 1,200 times. If charged once a day (calculated at 0.8 cycles), they will reach the critical point of life in about 3 years.
Lithium iron phosphate battery: The cycle life is approximately 1,200 to 2,000 times. When used at the same frequency, it can last for more than 5 years.
Estimation formula: Annual cycle count = Weekly charging count ×52 weeks; The remaining lifespan = (total number of cycles - number of used cycles) ÷ number of cycles in a year.
Iii. Professional Inspection: Penetrating "Surface Phenomena" with Tools
1. Core parameter detection (requires professional equipment at a repair shop)
Actual capacity: Through the discharge test with a "capacity detector", if the actual capacity is less than 70% of the rated capacity (for example, a 20Ah battery has less than 14Ah left), it indicates that the battery has severely aged and cannot meet the daily commuting needs.
Cell consistency: The voltage difference between each string of cells in a normal battery should be less than 0.05V (for example, a 48V battery is composed of 13 strings of cells, with each string having a voltage of approximately 3.7V, and the difference should be controlled within 0.05V). If the voltage of a certain battery cell is more than 0.2V lower than that of others, or if the voltage fluctuates sharply, it indicates that the battery cell is damaged and will affect the performance of the entire battery pack.
Internal resistance change: The internal resistance of a new battery is usually 20 to 50 milliohms. After aging, it may increase to over 100 milliohms. The greater the internal resistance, the more severe the heat generation during charging and discharging, and the more obvious the decline in battery life.
2. Functional verification of the protection board (BMS)
The protection board is the "safety guardian" of the battery. If the following situations occur, it indirectly reflects the aging of the battery:
Frequent triggering of "overcurrent protection" : Sudden power failure during acceleration while riding, and recovery after restart, indicates that the battery cell cannot withstand the large current output, and the protection board forcibly cuts off the power.
Premature power-off during charging: If the charger stops working before it is fully charged, it may be that the protection board detects an abnormal voltage (too high or too low) of a certain battery cell and terminates charging in advance.
Summary: When must the battery be replaced?
When any of the following situations occur, it is recommended to replace it immediately:
The range has been reduced to less than 50% of that of a new battery, and mechanical faults of the vehicle (such as motor aging and insufficient tire pressure) have been ruled out.
The battery shows signs of bulging, deformation, or becomes significantly hot during charging and discharging (exceeding 50℃).
Professional testing shows that the actual capacity is less than 70% of the rated capacity, or the voltage difference between the battery cells is greater than 0.2V.
The service life exceeds the designed service life (such as over 5 years for ternary lithium and over 8 years for lithium iron phosphate), and frequent power outages and power discharges occur.
Timely replacement of aged batteries not only restores battery life but also avoids safety risks caused by cell failure - after all, the "end of life" of lithium batteries is often accompanied by an increase in safety hazards.
