We’ve all seen the too-good-to-be-true battery listings online: 18650 batteries claiming huge capacity for incredible prices. However, as I’m sure you’re aware, if it’s too good to be true, it probably is! Using this Battery Capacity Tester from Open Green Energy, you can get an accurate look at the real capacity of any batteries you purchase.
This is useful not only for separating genuine from fake batteries but also for checking the health of batteries over time. After many charge/discharge cycles, all batteries start to lose capacity, and by comparing the real capacity to the label you can get an idea of how much life the battery has left. Once the capacity drops below 70-80% of the nameplate capacity, the battery is starting to near the end of its life. Different battery types and chemistries have different lifetimes and charge requirements, and it’s important to keep that in mind when conducting testing like this.
But for a quick look at your batteries, this board is more than sufficient. It uses an Arduino to control a simple constant-current circuit which drains the battery at a user-selectable rate. This allows you to see how capacity changes depending on discharge rate — higher discharge rates don’t allow the battery to expend all of its stored charge as efficiently, lowering the measured capacity. Discharging at a much slower rate will allow the battery to fully utilize its capacity. Charge and discharge rates are often stated in terms of C, which is the nameplate capacity in mAh. For example, discharging a 2.2Ah cell at 0.5C means discharging it at 1.1A.
If you want to learn more about Lithium batteries (and batteries in general) a great website to check out is Battery University. The website is full of useful information on battery testing and different battery chemistries. Learning about the battery chemistry you are using will help you utilize tools like this capacity tester, and help you interpret and characterize the results, giving you more confidence in your battery-powered designs!
