Consumer marketplaces like Amazon, eBay, and AliExpress are full of sellers selling fraudulent products. This is especially true for batteries, as most consumers don’t have the knowledge or tools to test them. If you buy a lithium battery (or a product containing a lithium battery), there is a high chance that you will be scammed, or at least the battery will have a much lower capacity than specified. The consequences can range from nuisance to legitimate danger. To prevent that, Open Green Energy has designed a DIY 18650 battery tester that anyone can assemble.
The purpose of this device is to allow manufacturers to easily test 18650 lithium batteries to determine their capacity. If the seller advertises the battery as something like 9900mAh, you can verify that using a tester. You can estimate the actual capacity (e.g. 3500mAh) fairly accurately. In this example scenario, you would return the battery and avoid that seller in the future. There is no problem if the capacity matches the specifications. But you might be surprised at how many sellers mislabel their batteries.
Open Green Energy previously shared a similar device, the Battery Capacity Tester V2.1. Its job was to safely discharge an 18650 battery (or any other battery) and measure the total power used. Assuming the battery starts with a full charge, that is the capacity of the battery. However, that device could not charge the battery, which was a bit of an inconvenience.
To make things a little easier, this new version allows you to both discharge and charge 18650 lithium batteries. Only one battery can work at a time (otherwise it’s dangerous), but it’s great for testing random samples from newly purchased batches.
The tester is built on a custom PCB that hosts a Seeed Studio XIAO ESP32 development board. Displays status and measurement data on a small OLED screen. The ESP32 has Bluetooth and WiFi onboard, making it possible to create smartphone apps to work with the tester in the future. At the moment, there are several modes, but in our opinion, the most convenient is the “Analyze” mode. This fully charges the battery and fully discharges it (to a safe voltage level) to determine the battery’s capacity. This makes testing your battery as easy as possible.
