21700 and 18650 choose to advance wireless technology
Here we focus primarily on tools and equipment for the construction trade. This makes the 21700 vs. 18650 Li-Ion conversation very relevant to us. After all, these lithium-ion power supplies go far beyond the latest cordless tools. They are driving innovation in Tesla, hoverboards, the vaping community, and more.
21700 vs. 18650: What do the numbers mean?
21700, 18650, 20700, etc. just refer to the physical size of lithium-ion batteries. For 18650 it is 18mm diameter x 65mm length. 21700 is 21mm x 70mm. While the explanation is simple, the difference is profound. It's easy to see with a quick volume calculation.
18650
3.14(9 x 9)(65) = 16,532 cubic millimeters
21700
3.14(10.5 x 10.5)(70) = 24,233 cubic millimeters
The extra 5mm of length and 3mm of diameter gives us a 47% increase in volume. That's a little more than 7,700 cubic millimeters of space to accommodate the energy-transporting anode, cathode, and electrolyte materials.
More capacity = more uptime
The most obvious benefit of using the 21700 over the 18650 is that the extra density means they have more energy available to keep your tools and gear running for longer. We see batteries using 18650 cells for power tools ranging from 1.5Ah (1500mAh) to 3.0Ah (3000mAh) in each cell. Issues have been reported with 18650 batteries at the top end of the scale, and 2.5Ah (2500 mAh) batteries seem to be the preferred choice for most manufacturers.
On the other hand, for power tool batteries, a 21700 battery starts at about 3.0Ah (3000mAh) and goes up to 4.0Ah (4000mAh). That's why we see compact (1P) battery packs from 3Ah or 4Ah all the way up to 12Ah (3P) big boys.
From the point of view of comparing 21700 vs. 18650 in power tools, you are looking at a 50%–100% increase in run time over today's standard 18650 battery packs. Outside of the power tool industry, some of these batteries go up to 5.0 Ah (5000mAh).
Current standard power tool batteries (based on 18V/20V max battery)
18650 lithium-ion battery cell
- Compact 1P battery: 2.0Ah–3.0Ah (36 Wh–54 Wh)
- Universal 2P battery: 4.0Ah–6.0Ah (72 Wh to 108 Wh)
- High capacity 3P battery: 9.0Ah (162Wh)
21700 lithium-ion battery cell
- Compact 1P battery: 3.0Ah–4.0Ah (54Wh–72Wh)
- Universal 2P battery: 6.0Ah–8.0Ah (108Wh–144Wh)
- High capacity 3P battery: 9Ah–12Ah (162Wh–216Wh)
21700 battery for more power
Batteries like the Bosch Core18V, Milwaukee M18 High Output, and Metabo LiHD battery packs do more than take advantage of longer run times. They have improved the cooling capabilities of the pack and used better materials to reduce electrical resistance (in ohms). The result is a battery with more usable power.
Take Bosch, for example. Their standard 18V battery can produce up to 800 watts of power output. When they upgraded to Core18V, the power went up to 1440 watts – an 80% increase in power! Other brands have also reported significant power gains.
It allows them to produce cordless tools that we thought a few years ago without wires. Many of them are now outperforming their wired counterparts.
Power tools are hardly the end product. Thanks to the 21700 lithium-ion battery cells, outdoor power equipment for lawn care and landscaping, battery-powered inverters and battery-powered construction equipment are all starting to have cordless options.