There is an indicator light on the front of your telephone modem:
A solid light indicates the battery is in good condition and fully charged.
A blinking light indicated your battery is charging. If the light continues to blink after 8 hours, your battery may be weak and may need to be replaced.
If the battery light is out on the modem device, your battery may be missing, depleted, or not correctly installed.
If an external battery/UPS is in use, please refer to the manual for that device.