Relationship Between Lithium-ion Battery Voltage and 18650 Battery Capacity
The 18650 battery is a standardized lithium-ion battery developed by SONY. Its dimensions are 18 mm in diameter and 65 mm in length, which have made it a benchmark in the industry. The battery is widely used in various electronic devices due to its large capacity, stable performance, and rechargeable properties.
18650 Lithium-ion Battery Voltage and Capacity
There are two common types of 18650 batteries:
- Lithium-ion batteries: Nominal voltage of 3.7 V, with an end-of-charge voltage of 4.2 V.
- Lithium iron phosphate (LiFePO4) batteries: Nominal voltage of 3.2 V, with an end-of-charge voltage of 3.6 V.
The capacity of 18650 lithium-ion batteries typically ranges from 1200 mAh to 3350 mAh, with most common capacities being 2200 mAh to 2600 mAh.
Applications of 18650 Li-Ion Batteries
These batteries are widely used across many fields:
- Laptop batteries due to their high energy density.
- Flashlights, wireless transmitters, portable medical equipment, industrial tools, and electric wearables benefit from their reliability and long charge cycles (around 1000 cycles).
The Relationship Between Lithium-ion Battery Voltage and Power
Battery voltage is directly related to the remaining capacity or charge level of the battery. As the battery discharges, the voltage drops, giving a measurable indication of how much charge is left.
Here is a typical voltage-to-capacity relationship for a 3.7V 18650 lithium-ion battery:
- 100% — 4.20 V
- 90% — 4.06 V
- 80% — 3.98 V
- 70% — 3.92 V
- 60% — 3.87 V
- 50% — 3.82 V
- 40% — 3.79 V
- 30% — 3.77 V
- 20% — 3.74 V
- 10% — 3.68 V
- 5% — 3.45 V
- 0% — 3.00 V
Factors Affecting Voltage and Capacity
While measuring battery voltage is a common method for estimating remaining battery capacity, certain factors affect its accuracy:
- Discharge Current: Higher discharge currents lead to lower voltage, even if the battery’s actual capacity is higher.
- Temperature: At lower temperatures, battery voltage decreases, even if the capacity remains constant.
- Battery Cycle: With more charge-discharge cycles, the battery’s discharge platform deteriorates, resulting in lower voltage readings for the same capacity.
- Manufacturer and Battery Chemistry: Different manufacturers and battery chemistries (e.g., lithium cobalt oxide vs. lithium manganese oxide) have slightly varying discharge platforms.
Conclusion
The voltage of a lithium-ion battery, such as the 18650, is a key indicator of its remaining capacity. However, due to factors such as discharge current, temperature, and battery aging, voltage alone cannot be solely relied upon for accurate capacity estimation. Understanding these variables allows for better management and usage of lithium-ion batteries in various applications.
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