In my e-bike class I discuss the ubiquitous 18650 lithium-ion cell used in most e-bike batteries today. These batteries have been around for a while and are used in many laptop computers, cordless power tools, some electric cars, electric kick scooters, most e-bikes, portable powerbanks, electronic cigarettes, and some LED flashlights. This broad acceptance usually translates into lower cost and improved quality/reliability.
So, the question is, if the 18650 cell is working so well, why change? And what’s next for e-bikes? Good question! I’m glad you asked…
Having done some research, there are a few factors to consider when selecting certain types of batteries for your e-bike. One factor is ‘space’. It’s likely that you be using a 18650 cell pack if you’re cramped on space. The cells are slightly smaller than the next cell configuration, the 21700 cells that are also fairly common these days, but are a bit more expensive than the 18650s, and tend to be used in applications that require more energy and can tolerate greater weight and space than a battery pack using the 18650 cells.
Here’s a short thread that discusses the differences between the 18650 and 21700 cells:
From this link, I quote:
“21700 cells use the same tech as 18650 cells meaning it delivers the same power per weight, but just by size comparison the 21700 cell is 46% more bigger.
Both have same voltage, but 21700 cells can deliver 40% more power via capacity and amperage.
If you want power, slim build, and less capacity for cheap, get 18650
If you want the same power, bulkier build, and travel 40% farther, worry less about overheating at a premium, get 21700s”
And summarized from a recent e-mail exchange with Matt Robertson (Tales On Two Wheels):
Matt has been using both battery configurations in his builds. His Bullitt (ebike) uses a custom 32ah Samsung 35E cell pack, which are 21700 cells. And the Luna V2 (used for his Apostate build) is using 18650’s. The pack on the Apostate was chosen primarily because it was a perfect fit for the frame. Everything else was secondary… you can get more details about his rationale for using the Luna V2 battery for this build in his recent Day 3 article.
Matt continues:
“At this point in time, 21700 cells are superior but not hugely so. Its not enough of an improvement to be the sole decision maker. As you can see above, that one pack had a number of things going for it and cell content was secondary. Those cells have been available for some time but have not taken over the world. Primarily due to cost.
It really depends on what you are looking to do with the battery, how big it is. How expensive the cells are when making your buy decision.”
Which brings us to a relatively recent development in battery tech that could find its way into the e-bike market, and that’s LiFePo4. LiFeP04 (lithium iron phosphate) tends to be less energy dense and heavier, but a pack can be charged up to 100% and left there for extended periods, and those packs are good for 2000-3000 cycles whereas a li-nmc/18650/21700 pack is going to live about 400 cycles (worse case). Also there is no explosion or fire risk. BTR Power is selling them on Amazon for e-bike batteries although they really are better suited for ‘cargo’ bike apps where you can live with a bigger battery.
Well that’s all I know about e-bike batteries for the moment, and my head hurts from thinking about this topic. Many thanks to Matt Robertson for steering me in the right direction to help y’all learn a bit about battery tech. And for the moment, I have a lot invested in 18650 battery packs, so I guess I’m just going to use those up before I switch to any of the newer battery tech. And maybe by then there will be something better and cheaper on the market anyway. With all the innovation happening in the EV automotive space, there’s likely to be trickle-down into the e-bike segment, especially for the ‘performance’ e-bike market. I was viewing a YouTube video recently (Future E Bike Technology Part 3) where a comment was made that most ‘serious’ mountain bikes in the future will have some ‘e’ components. To get there though, battery weight needs to decrease, range needs to increase, and e-mountain bike (eMTB) systems need to improve.
Exciting stuff for sure!