BETA

Introduction

I’m not a big fan of lithium-ion 18650 cells, as they are not an ideal way to power devices. Their energy density is on average, and they usually require additional mounting components such as battery pads or plastic holders, which take up valuable space. The capacity limit per cell is also a factor, you can realistically achieve up to about 3500 mAh from a single cell. For recycled batteries, anything between 2000 and 3000 mAh can be considered a good result.

And no, there are no 18650 cells with 5000–10,000 mAh capacity. If someone claims otherwise, that’s simply not true.

In my opinion, buying new 18650 cells often doesn’t make much sense. You usually get better price-to-performance by purchasing flat LiPo packs instead. The only real advantage of using 18650 cells in a build is economic. If you have access to recycled cells, or you know how to safely recover them yourself, then it can make sense.

This site will not provide information on how to extract 18650 cells from old laptop batteries or vacuum cleaners. That process is potentially dangerous and requires experience.

If you plan to erecover used cells, you do so at your own risk.

if you do this wrong enough, it can lead to short circuits, electrolyte leakage, burns, or even fire. You need to be aware of this!

The only reason I use 18650 cells in my DIY projects is that I have some experience with them and I had a large stock left over from previous projects (so it’s purely an economic aspect).

If you’re planning to buy new batteries, don’t even consider 18650 cells, move to the flat LiPo packs section instead.

Battery packs

If you need more than the 3000–3500 mAh limit to power your node for a longer time, you’ll need to use a larger 3.7 V flat pack or conect a few 18650 cells into a pack. There are two ways to connect cells in a pack: series and parallel. Series increases the voltage, while parallel increases capacity, keeping the voltage of a single cell.

Boards used for Meshcore generally require a voltage below 5 V, so connecting cells in series (and multipliing the voltage) doesn’t make much sense. To achieve the required voltage, you would need additional components like a step-down converter, which increases build complexity and causes losses (each voltage conversion generates losses and usually heat, which doesn’t make sense for battery-powered devices enclosed in a sealed case).

In my builds, I’ll use a parallel connection, which maintains the desired voltage but unfortunately gives other issues.

• Batteries connected in parallel cannot be charged together. You must disassemble the pack and charge them separately. Charging them together can lead to overcharging, which may cause overheating and permanent damage.

• Cells used to build a pack must have similar capacities. Differences can lead to excessive discharge and permanent damage to a cell.

• Connecting cells into a pack requires using batteries with the same voltage. Differences in voltage will cause a rapid flow of high current between the cells, which can lead to heating, cell damage, or sparking.

• If you reverse the polarity of a cell in a pack, the current will flow rapidly and spectacularly.

Do I recommend building packs with 18650 cells?

Definitely not if you don’t have experience.

If you do have experience, you’ll know best how to handle them yourself.

Tools

• Batteries of this type require a proper charger that allows current adjustment and has funcions, like capacity test, charge, and discharge. I personally have several LiitoKala Engineer Lii-500 units. They meet my expectations and are durable.

• A multimeter

Testing

Factors that diqualify a battery for use.

• Overheating during charging. Any temperature that is clearly noticeable by hand during charging or discharging, even at a low current, is disqualifying.

• Corrosion (often indicates electrolyte leakage).

• Self-discharge of the battery: if the voltage drops more than 0.2–0.4 V after 2–3 weeks, the electrolyte is most likely already degraded, or there are internal shorts.

• A capacity below 1500 mAh usually doesn’t make sense.

• Discharging a battery below 2.5 V usually causes permanent electrolyte degradation. The battery’s capacity decreases, and faster self-discharge may occur. Avoid over discharging.

Cost

A few euros per cell, depending on the brand and capacity. In my opinion, it’s not worth.

Recycled cells can be free if you have a source, but that requires experience.