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Fibre Home Phone service: Questions about the battery back-up unit

What is the battery back-up?

A battery back-up unit (BBU) may be provided by the engineer when your Openreach fibre modem is installed. If provided, it enables your fibre home phone line to continue working in the event of a mains power cut in your home. This means you will still be able to make and receive calls for up to an hour.

It's powered by four rechargeable AA batteries which we provide as part of the initial installation. It's your responsibility to make sure the batteries are charged and to replace them when necessary.

The battery back-up unit is charged by your Openreach fibre modem. So it's really important to leave your modem plugged in and switched on. Otherwise your batteries won't stay charged up and you won't be able to make outgoing calls if there's a power failure.

Note that the battery back-up unit doesn't provide any power to your cordless phones. You'll need to have a corded phone plugged in to use if there's a power outage.

You'll need to replace the batteries in the battery back-up unit when the 'FAULT' light goes red.

What do the lights on the battery back-up unit mean?

Light Light status What to do
STATUS Green The battery back-up unit is working correctly
Off Please connect the battery back-up unit to the power socket
FAULT Red Please replace the battery
Off The battery back-up unit is working correctly
CHARGING Yellow The battery back-up unit is charging
Off The battery back-up unit is working correctly

How do I change the battery in my battery back-up unit?

Replacement batteries need to be nickel metal hydride (NiMH rated at 2000maAh or above). We'd recommend that you keep a spare set in the house. They can be purchased from most shops that sell batteries.

If the front of your battery back-up unit has a sliding cover:

  1. Slide the front cover to the left
  2. Remove the four rechargeable AA batteries
  3. Install the replacement batteries, being sure to place them the right way
  4. Replace the cover, sliding to the right to close

If the front of your battery back-up unit doesn't have a sliding cover:

  1. Slide the battery back-up unit up and forward to release it from the wall
  2. Turn the unit over and slide the cover up and off
  3. Remove the four rechargeable AA batteries
  4. Install the replacement batteries, being sure to place them the right way
  5. Replace the cover, sliding to the right to close
  6. Fix the unit back on the retaining screws and allow to drop down

Will my service work if the battery back-up unit is not working?

If the batteries fail in the battery back-up unit, the Openreach fibre modem will continue to work so long as it has mains power, but you should replace the batteries as soon as possible.

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