What’s in an eMTB battery?Currently, most eMTB batteries are 18650 lithium-ion (Li-ion). Li-ion batteries were first developed in 1985 and they were the main driving force behind the development of electric vehicles because they are rechargeable and you can get a lot of power without taking up too much space.
The 18650 part refers to the cells of the battery. Each battery is filled with individual cells that measure 18mm x 65mm, roughly the size of your finger. These are soldered together in packs which are connected in parallel. If you take the plastic shell off, it looks a bit like a bunch of AA batteries all together.
What goes inside the battery is not that important, but there is one important number with batteries: watt hours. This, as you might expect, is a measure of how many watts can be delivered in an hour. So, for example, a 250 watt-hour battery could run a 250 watt motor at full power for one hour, while a 500 watt-hour battery could run it for 2. Most e-bike batteries are range between 300 and 550 watt hours. The gold bullet with the batteries gets as many watt hours as possible, but if you keep adding cells you will start to add weight and bulk.
Tesla does not currently use 18650 cells, however; it now uses the 21700 standard with cells measuring 21 mm by 70 mm. Tesla developed this cell with Panasonic in 2017 and its larger volume means it can be packed with more anodes and cathodes to hold more energy. Tesla also claims it has a longer lifespan because it needs to be charged less.
We’ve recently started to see these cells entering eMTBs, with Specialized’s Turbo Levo Kenevo being the one we’ve covered the most on Pinkbike. This bike has a massive 700 Wh battery, making it one of the biggest you can get on an eMTB today.
Tesla hasn’t stopped 21700 however, and its announcement on Tuesday is the next evolution of its cellular technology.
How is Tesla’s new battery different?
The new Tesla battery has grown in size again, this time much more significantly to 4680 or 46mm x 80mm. However, the real innovation comes from what’s inside the box. Standard 18650 and 21700 cells use 2 tabs connected to thin pieces of copper and aluminum foil to connect battery operation to the outside world. Not only are these tabs complicated to manufacture, they also take up space inside the battery and reduce efficiency as current has to travel the entire length of the electrode to reach each tab.
Tesla’s new design does away with those tabs and instead uses a “spiral shingle” design to collect current, which reduces internal resistance, cuts costs, and simplifies manufacturing. Musk said, “The distance the electron has to travel is much less. So you actually have a shorter path length in a large cell with no tables and then a smaller cell with tabs. So even though the airframe is larger, it actually has a better power to weight ratio. “
According to Drew Baglino, senior vice president of powertrain and engineering at Tesla, the innovations increase the energy five-fold, the horsepower six-fold, and the range of a car using those batteries by 16 percent. It’s worth saying that we don’t know what the baseline is for these numbers as no exact number is given, but we assume it is against the 21700.
Will we ever see this on eMTB?
The benefits for eMTBs of a more powerful battery are obvious. You can either deliver the same power in a smaller, lighter package, making the grip of the bike and more like a traditional mountain bike, or you can keep the same battery size and increase the range of the bike.
As impressive as Musk’s claims were, there was a problem. While the cells are apparently currently in testing, no physics have been shown and it will apparently be another three years before the technology is released. Also, don’t expect eMTBs to use them right away. It took about 2 years for the 21700 technology to spread from Tesla Model 3 cars to the Specialized Kenevo, so you can probably expect the table-less batteries to be the same, if that even happens.
There are also reasons bike makers are currently happy with the 18650 system and see no reason to change. There is still a lot of innovation in this cell size with Bosch unveiling its Powertube 625Wh battery last year, offering a huge range despite the smaller cell size. The internal components of these cells are also being refined, with engineers experimenting with different cathode and anode materials to increase capacity.
One of the other big problems with increasing the volume of a cell is that it is more difficult for heat to escape. If a battery becomes too hot, it must operate at reduced power or risk permanent damage. Electric ATVs are often exposed to the sun all day long, so the better heat management of an 18650 cell could lead to better performance over a longer period of time.
Finally, as with all things, cost will surely be a factor. 18650 cells are proven technology, have now been perfected for cycling applications, and are widely produced by a number of competing brands. New tech rarely comes cheap, especially in its early days, and while Musk is aiming for a $ 25,000 electric car, we doubt he’ll let that competitive advantage slip away easily.
So, will eMTB batteries get smaller, lighter, cheaper and more powerful? Almost certainly. Will it be because of Elon Musk? Probably not for a while at least.