Hi Leonti, thanks for the feedback! We understand that a lot of users are concerned about battery percentages and we appreciate the chance to clarify for everyone.
Sesame's battery percentage is currently based on voltage rather than remaining capacity, which accounts for much of the (understandable) confusion on the part of our users.
Here's an example of what the curve will look like for lithium batteries:

Since the voltage doesn't drop much for much of the battery's lifespan, it's normal for the percentage on your Sesame to show as 100% for a long time, due to your batteries' voltage being higher than the level set as max voltage. There may be fluctuations in voltage, but rather than showing the battery percentage as 102% or 105%, the maximum is capped at 100%.
Once the battery percentage on Sesame begins dropping, it means that the voltage is dropping quickly because the battery is nearing the end of its lifespan, so please be sure to change your batteries when the percentage is no longer nearing 100%. Our low-battery notifications are sent at 40%, and we recommend changing the batteries as soon as you receive the notification, as Sesame will stop working when batteries get even lower in order to protect the hardware from getting damaged due to insufficient power.
Please note that these numbers were determined using Panasonic CR123A batteries, which is why we recommend our users continue using Panasonic batteries for best results regarding battery life estimates.
If your battery percentage is dropping from 100% very quickly, this may be due to defective batteries or an issue with Sesame. In these cases, we recommend you write to us at sesame@candyhouse.co (and be sure to provide the email address associated with your Sesame account) so we can take a look.
We understand that the current battery percentage curve on Sesame is unintuitive and likely to cause confusion for our users, as most users would expect the battery percentage to be based on capacity rather than voltage. Our product development team is aware of this issue and are working on solutions, so hopefully we will be able to offer an update soon that will make the battery percentage more intuitive to our users.
Thanks again for using Sesame and for your kind words, and for the opportunity to clarify the issue with battery percentage. Please don't hesitate to let us know if you have any suggestions or further questions regarding Sesame. We'd be happy to help! - CANDY HOUSE