Li-ion Batteries
When we say "Li-ion" battery, what we mean is "a battery composed of li-ion cells". One li-ion cell might be enough to power a small LED lamp, but we need way more than that to power an electric skateboard.
Li-ion battery cells come in various shapes and sizes. We'll focus on the most used for esk8: the 18650 cell.
The 18650 name comes from the size of the cell: 18mm x 65mm. It's like a bigger AA battery (an AA battery is 14mm x 50 mm).
They are very common, you can find them in old laptop batteries or even in Tesla cars. They are made by different manufacturers and their characteristics greatly varies depending on the manufacturer and/or model.
Depending on your needs, li-ions can be considered better than lipos. They have a better lifespan (more charge/discharge cycles before going bad). They are also safer, thanks to some protection mechanisms (see this blog post) and also because of their metal enclosure (less prone to be pierced or damaged by external elements). Li-ion cells are also better at sitting for a long period of time (lipos also can stay stored for a long period, but they need to be stored at the right voltage to keep them in good shape). All those advantages make them a good choice for mainstream products.
Although the price per cell might look attractive, you need quite a bunch to get a decent battery for an esk8, and you still need to assemble the cells using nickel strips and a spot-weld them in place. In the end, lipos are still the cheapest option. You can buy pre-built packs too, but prices are way higher than lipos at this point.
The voltage of a li-ion cell goes up during charge and goes down during discharge. A li-ion cell nominal voltage is 3.6 volts. A fully charged cell is 4.2V. A discharged cell can go as low as 2.5V, but you should not get them that low, try to stay above 2.8V. Going below might damage your cells or get bad voltage sag while riding. Li-ion cells are made differently depending on the manufacturer, and each can have different characteristics so be sure to check those out before referring to this table.
| Battery | Nominal V | Full charge | Minimum V | Recommended min. V |
|---|---|---|---|---|
| 1S Li-ion Battery | 3.6V | 4.2V | 2.5V | 2.8V |
| 2S Li-ion Battery | 7.2V | 8.4V | 5.0V | 5.6V |
| 3S Li-ion Battery | 10.8V | 12.6V | 7.5V | 8.4V |
| 4S Li-ion Battery | 14.4V | 16.8V | 10V | 11.2V |
| 5S Li-ion Battery | 18V | 18.5V | 12.5V | 14V |
| 6S Li-ion Battery | 21.6V | 25.2V | 15.0V | 16.8V |
| 7S Li-ion Battery | 25.2V | 29.4V | 17.5V | 19.6V |
| 8S Li-ion Battery | 28.8V | 33.6V | 20.0V | 22.4V |
| 9S Li-ion Battery | 32.4V | 37.8V | 22.5V | 25.2V |
| 10S Li-ion Battery | 36.0V | 42.0V | 25.0V | 28.0V |
| 11S Li-ion Battery | 39.6V | 46.2V | 27.5V | 30.8V |
| 12S Li-ion Battery | 43.2V | 50.4V | 30.0V | 33.6V |
Li-ions don't have a C rating like lipos do, but they have a continuous discharge rating, measured in amps. Again, that characteristic depends on the manufacturer. Don't believe anything you see, cheap manufacturers often indicates fake CDR to attract customers.
The capacity means how much energy you can store in the battery, often stated in mAh (milli amp hours) or Ah. 18650 cells are all the same format, so you won't see huge capacity difference between a model and another. Capacities range from 1800mAh to around 3500mAh.
If you want to know more about the different 18650 models on the market, this site contains charts for dozens of brands and models and allows you to compare them.
If you want to use li-ion cells for your setup, you have 2 options:
- buy cells separately and assemble the battery pack yourself
- buy a pack already assembled
Here’s a topic on a 10S 18650 cells battery build.