Hi Fredrik, as you can see on the quick guide, with the battery sensor you can have only message when the battery be up or under a specific treshold. For 24V the threshold is 23.1V (± 0.3V).
Here whant the Quick guide tell abaut this.:
The ZigBoat™ Battery Sensor monitors the battery power bank voltage and, if it drops below a fixed threshold sends you push notifications. Thanks to the switch you can use 12V or 24V battery power bank. NOTE: 12Vmode threshold: 11.6V (± 0.3V) 24Vmodethreshold: 23.1V (± 0.3V)