The battery life of Whistle 3 will vary based upon how it is used and how often it is within range of Wi-Fi.
Whistle 3 lasts an average of 7 days on a single charge.
When Whistle 3 is in one of your designated places with Wi-Fi, it will switch to power save mode. This is when the device communicates minimally in order to conserve battery.
You can check if your device is in power save mode by looking at the Location page in the Whistle app. If you've confirmed that your device is in power save mode while in your designated places, then you should get the appropriate battery life per your usage of Whistle 3.