How will I know when the battery is worn out and needs replacing?

If the battery needs to be replaced, the nbn™ Power Supply with nbn™ Battery Backup will beep every 15 minutes. This alarm can be silenced for 24 hours by pressing the alarm silence button.
 
nbn tests your battery remotely every 55 days. If your battery charges to less than 70% of its original capacity nbn will alert your phone, or they will alert your internet service provider who will then alert you. This should occur well before the battery is close to failing.
 
You should replace your battery if you receive this alert – if you do not, nbn will continue to contact your phone or internet service provider every two weeks for 18 weeks.