The lithium-ion battery industry has seen rapid innovation in recent years to keep up with ever-increasing power demands. Two of the most popular battery sizes are the tried-and-tested 18650 and the newer 21700. But when it comes to 21700 battery vs 18650 battery, which one reigns supreme?
In this comprehensive battery comparison guide, as a professional 21700 battery pack and 18650 battery pack manufacturer, we’ll analyze the differences between 18650 battery and 21700 battery, from physical size and capacity to performance and cost efficiency. By the end, you’ll know exactly how to choose the right Li-ion battery for your application’s power and runtime needs.
Key Differences Between 21700 and 18650 Batteries
To understand 21700 vs 18650, let’s first break down what the numbers mean.
18650 refers to a cylindrical lithium-ion battery with a diameter of 18mm and a length of 65mm. 21700 simply means a 21mm diameter and 70mm length cell.
So at first glance, the 21700 is larger in physical size. And with more internal space, it can hold substantially more battery chemistry. Specifically:
- 21700 batteries have up to 5000 mAh capacity compared to just 3500 mAh for 18650s — a 40% increase!
- This also translates to a higher energy density around 300 Wh/kg vs 250 Wh/kg for the best 18650s on the market.
- The extra capacity means 21700 cells can safely deliver 50% more power (over 10 amps) versus 18650 topping out around 7-8 amp continuous draw.
On paper, 21700 clearly beats 18650. But keep reading to understand the real-world tradeoffs.
21700 Battery vs 18650 Battery
18650 vs 21700: Comparing Physical Properties
The 21700 battery’s bigger physical size is both a strength and a weakness compared to 18650:
Pros:
- Higher energy density as mentioned earlier
- Lower internal resistance enables better power delivery
- More surface area improves heat dissipation
Cons:
- Large diameter cells don’t fit existing 18650 battery slots
- Longer 70mm length may not work in compact enclosures
- Often costs more per cell than mass-produced 18650
So while 21700 has clear performance advantages, retrofitting devices like laptops and power tools requires extensive redesigns. And the longer 21700 cells may not work in ultra-slim gadgets.
18650 vs 21700: Performance Comparison
Now let’s compare how these physical differences actually affect real-world usage and device runtime.
We’ll use an example of the popular Acebeam X50 flashlight available for either 21700 or 18650 batteries with included cell adapter.
21700 battery installed
- 5000 mAh Samsung 50E
- Max 1500 lumens turbo mode for 2 minutes
- 1000 lumen high mode for 145 minutes
18650 battery installed
- 3500 mAh Samsung 35E
- Max 1000 lumens turbo for 2 minutes
- 1000 lumen high mode for 95 minutes
The runtime increase is over 50 minutes in the highest sustainable setting despite identical lumen output. This huge boost is possible solely thanks to the 21700 battery’s superior capacity in the same flashlight body.
And that’s just one 21700 vs two 18650 configured for equivalent 12.4V. With bigger devices supporting multiple cells, the runtime advantages grow even further.
Clearly, the 21700 battery technology enables much longer runtime along with higher peak power. But what about the cost comparison?
21700 vs 18650: Price Per Performance Ratio
It’s quite surprising, but most 21700 batteries have excellent price-per-capacity ratios despite being newer to market.
Let’s consider a real-world 21700 vs 18650 pricing example for DIY battery builders:
Samsung 50E 5000 mAh 21700 – $6 per cell
Samsung 35E 3500 mAh 18650 – $5 per cell
Despite being rated for 30% extra capacity over the 18650, the 21700 cell is only 20% more expensive. You could build a 6S2P pack with 12 Samsung 21700 cells for $72 and get 10,000 mAh capacity.
A pack of equivalent capacity with 18650 35E cells would require 16 cells for $80! So you save money despite gaining an extra cell slot for future expansion.
Clearly, the 21700 battery outpaces 18650 on both performance and value metrics. But what about safety and reliability?
Battery Safety: 18650 vs 21700
With ultra-high energy density lithium cells, safety is paramount. How do 21700 and 18650 compare by this vital metric?
Broadly speaking, both modern Li-ion battery types have excellent safety records when produced by reputed brands. For example, going with a quality 21700 cell like the Molicel P42A avoids safety risks from no-name cells.
However, historically the 18650 form factor has better consistency across manufacturers. The 21700 battery space is still shaking out low-quality offerings which led to isolated incidents like battery fires.
But despite a higher safety risk perception, 21700 popularity is growing exponentially. Top manufacturers like Samsung, LG, and Panasonic already have great quality control. And early issues faced by any new technology eventually get ironed out.
So both battery types are fundamentally safe when you pick an authentic cell from established brands. Regarding stability and cycle life, 18650 and 21700 are again on par with 500 cycles plus being common.
Conclusion
To summarize this detailed 21700 vs 18650 comparison guide:
- 21700 batteries beat 18650 in capacity, power capability and energy density thanks to larger physical size.
- The superior performance directly translates to longer runtimes with around 50% gains being possible.
- Despite being newer, 21700 cells already rival and sometimes beat 18650 pricing in cost-per-mAh.
So the 21700 battery is certainly the way of the future. However, the 18650 form factor has unmatched product compatibility today.
You can expect leading manufacturers to rapidly adopt 21700 cells across power tools, e-bikes, laptops, and even smartphones over the next few years. But old and new battery technology will coexist in near future keeping 18650 relevant for upgrades.
Overall my recommendation is starting new battery-powered device designs with 21700 lithium-ion cells. For legacy equipment, stick with 18650 until you’re ready to fully redesign and leverage 21700 energy density. This balanced approach will help you extract the best runtime and performance as applications transition to the next-gen battery platform.
