Think of your beacon(s) as most other battery powered devices. Your phone, for example, uses more power when actively used. If you continually monitor your beacon, it will consume more power than when CrewWatcher is disabled. In fact, if you turn CrewWatcher off ("disable") in the app, it will automatically put your beacon into sleep mode, consuming very little power.
So don't forget, if you are finished using the product, make sure you have disabled CrewWatcher in the app.
For safety reasons, the battery is not replaceable. The battery will usually last for 5 years of regular use, as long as the power is managed.