Apr. 09, 2025
Lithium-ion batteries, known for their high energy density and high voltage, have become the preferred energy storage solution across a range of applications, including mobile and wireless devices, power tools, and hybrid or electric vehicles.
Power tools that use standard lithium-ion batteries must be capable of high-rate discharge to meet the intensive demands of these tools. However, due to limitations in cost and materials, regular lithium-ion batteries often struggle to deliver the high-rate discharge performance required for power tools.
As a result, many affordable lithium power tool batteries on the market tend to underperform. You might notice that while the tool works fine immediately after a full charge, the power drops off quickly during use—leaving the tool feeling weak and lacking stamina. Additionally, these batteries generally offer poor resistance to high temperatures, leading to a shorter overall service life.
Compared to lithium-ion batteries, nickel-metal hydride (Ni-MH) batteries have lower energy density. This means that within the same battery pack size, Ni-MH batteries typically offer less capacity than their lithium-ion counterparts. However, Ni-MH cells provide better consistency, which translates to enhanced safety and stability in battery pack performance.
Ni-MH batteries are capable of delivering high discharge rates—up to 15C or more—making them well-suited to meet the demanding power requirements of most power tools.
While Ni-MH batteries are heavier than lithium-ion batteries, they come with the advantage of lower production and market costs, which helps maintain their competitiveness in certain segments of the power tool market.
That said, one major drawback is their poor low-temperature performance. Compared to low-temperature lithium iron phosphate and polymer lithium-ion batteries, Ni-MH batteries struggle in cold environments, making them less ideal for power tool applications in low-temperature regions.
Lithium iron phosphate (LiFePO₄) batteries offer several advantages when used in power tools. Notably, they exhibit superior high-temperature resistance compared to other lithium-ion battery types and support discharge rates exceeding 30C, ensuring strong performance in both standard and wide-temperature environments.
Compared to nickel-metal hydride (NiMH) batteries, LiFePO₄ batteries deliver significantly better low-temperature performance and higher energy density. Additionally, they boast a longer service life.
Unlike NiMH batteries, which suffer from a memory effect, LiFePO₄ batteries are free from this issue. However, current lithium iron phosphate technology still lags behind in some aspects—particularly in terms of battery consistency. As a result, battery packs made from LiFePO₄ cells may exhibit slightly lower safety levels compared to their NiMH counterparts.
Among all types of power tool batteries, polymer lithium-ion batteries are generally the most expensive. They offer the highest energy density and are particularly well-suited for ultra-high-rate discharge applications, making them ideal for demanding power tool operations.
The high cost of polymer lithium-ion batteries is primarily due to their use of rare, high-energy-density materials and the complex manufacturing processes required to produce them.
However, one drawback is their relatively poor high-temperature performance, which is slightly inferior to that of lithium iron phosphate batteries and comparable to nickel-metal hydride batteries.
Currently, most power tools still rely on 18650 lithium batteries as their primary power source. Nevertheless, with the emergence of 21700 lithium batteries, this trend is gradually changing.
The numbers 18650, 21700, 20700, etc., refer to the physical dimensions of cylindrical lithium-ion batteries. For instance, in a typical 18650 battery, "18" stands for the diameter in millimeters, "65" for the length, and the final "0" indicates a cylindrical shape. It’s worth noting that while 18650 batteries are commonly lithium-based, nickel-metal hydride (NiMH) batteries can also come in this size.
Compared to 18650 cells, 21700 batteries are 5 mm longer and 3 mm wider in diameter, resulting in a 47% increase in volume. This additional space—around 7,700 cubic millimeters—can be filled with more anode, cathode, and electrolyte material, which directly translates to higher energy storage. As a result, 21700 lithium batteries generally offer greater capacity and longer runtime than 18650 batteries, making them increasingly popular for high-performance power tools.
One of the most significant advantages of 21700 batteries over 18650 batteries is their increased internal space, which allows for more active materials—resulting in higher energy capacity and longer runtime for power tools.
For example, 18650 cells typically offer capacities ranging from 1.5Ah (1500mAh) to 3.0Ah (3000mAh) per cell. However, high-capacity 18650 cells (3.0Ah) have been known to encounter quality and consistency issues in mass production, leading many manufacturers to standardize around 2.5Ah (2500mAh) versions for better reliability.
In contrast, 21700 cells generally start at 3.0Ah and can reach up to 4.0Ah per cell. This increased capacity allows for more powerful and longer-lasting battery packs. As a result, we commonly see compact (1P) battery packs labeled 3Ah or 4Ah, and larger configurations (such as 3P) delivering up to 12Ah, offering extended operation time for heavy-duty tools.
The following section provides a comparison of the capacities of commonly used power tool batteries, including those based on ternary lithium chemistry, along with insights into their safety and performance.
18650 Battery Packs
- Compact 1P configuration: 2.0Ah–3.0Ah (36Wh–54Wh)
- Standard 2P configuration: 4.0Ah–6.0Ah (72Wh–108Wh)
- High-capacity 3P configuration: Up to 9.0Ah (162Wh)
21700 Battery Packs
- Compact 1P configuration: 3.0Ah–4.0Ah (54Wh–72Wh)
- Standard 2P configuration: 6.0Ah–8.0Ah (108Wh–144Wh)
- High-capacity 3P configuration: 9.0Ah–12.0Ah (162Wh–216Wh)
Note: The above values are calculated based on typical capacity ranges and do not consider the nominal voltage of the battery.
The 18650 lithium battery has long been a standard choice for power tools due to its balanced size, lightweight design, and proven reliability. In comparison, the 21700 lithium battery is larger and heavier but offers clear advantages in terms of higher energy capacity, stronger output, and longer service life.
Both battery types are suitable for power tools, and the best choice depends on your specific application needs. If portability and lighter weight are priorities—such as for compact or handheld tools—18650 batteries may be more appropriate. However, if you require longer runtimes and higher performance, especially for high-demand tools, 21700 batteries are the better option.
When selecting batteries, it's essential to choose reputable manufacturers to ensure quality, safety, and reliable after-sales support.
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