Lithium batteries discharge curve

Even though we don't manufacture lithium batteries, there are a few reasons you may find yourself wondering why the battery level may vary as much upon first days of delivery.

Let's first understand how we this level is calculated:

Battery Percentage Calculation

Battery readings are a result of voltage changes calculations, which have a +/-10% precision. It's not a perfect estimation by any means, but it can give you a sense of the battery level in order to identify when any needs to be replaced. And since Bluetooth Low Energy has a very small impact on it, it allows us to avoid adding a dedicated chip and rather translate this into a percentage level.

Battery Specification

Some fluctuations in these readings are expected, mostly due to how susceptible these batteries are to temperature changes. Beacons kept in cold spaces are more likely to give off a lower battery level (since batteries will drain faster below freezing point) than those stored at room temperature. The same applies for hot temperatures, a battery's performance will be affected on temperatures exceeding 30ºC (86F).

You can see the expected discharge curve on the following image:

Our Beacon (two batteries model), Tough Beacon, and Beacon Pro, all use a cr2477 3V lithium battery. If you would like to learn more about these batteries and their properties, check out this datasheet.

Production

Kontakt.io beacons are manufactured in our HQ offices in Poland, batteries are placed on the beacons by our production team and tested before being shipped. Because our beacons are permanently on from the moment they leave our production facility, they'll start using their battery and going through the initial discharge phase. It's important to know this in case you've planned to store your beacons for a while before deployment.

Tough beacons in particular, are given a special sealing method that makes them weather and waterproof, their batteries can't be replaced, so important consideration should be given to their configuration.

Configuration

The most important factor when talking about battery life, is the configuration of the beacons themselves. There are two parameters that highly affect the battery life: transmission power, and advertising interval. The combination of these two will determine the life of your battery, to maximize this, we recommend going for a higher advertising interval value, rather than reducing the transmission power; the latter may affect communication with your beacon later on, lower tx levels are only recommended on the deployment phase of your project.

To learn more about the default configuration used, and the estimated battery life you can achieve on the different configuration presets we have available, please visit our Beacon presets article.

Testing

We've found that while testing, battery life is affected by continuously writing new configurations. Changing a beacon's configuration involves establishing a connection, which isn't a beacon's main role of advertising their configured values, so there's a higher demand on every configuration attempt.

Once you know which configuration best works for your project, you can order beacons already pre-configured and ready for deployment. This will considerably save you time and more importantly, battery life.