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Message 1 of 6

Digital Voice, Smart hub 2 and BBU

Hi. I have moved into a new property with FTTP and just had my broadband activated today (Fiber 100). When ordering the package online it gave us the default option of upgrading to the Digital Voice service free with 2 phones free. The next page said in the event of a power cut we would need to purchase a BBU separately which i ignored as there is one already installed in the ONT box. 

I wrongly presumed the phones would have a base station or something that would go to the modem to be powered buy the BBU. 

What they actually do is link via wifi to the smart hub 2


this is copied from the bt help section which lead me to believe that maybe the bbu would power the hub by PoE as is says with the bbu you will still have broadband and phone

Digital Voice: I have a problem with my battery back-up unit (BBU)

Your Hub must have power for you to be able to make calls using our Digital Voice service. You can buy a battery back-up unit (BBU) when ordering Digital Voice. This means that both broadband and voice services will continue to work for at least an hour if there's a power cut.


Please make sure you keep your battery back-up unit connected to the mains power supply and your Hub powered up. This will make sure it has enough charge if it's needed.

Does any know how this system works as I cannot find much information and what in have found contradicts itself


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Message 2 of 6

Re: Digital Voice, Smart hub 2 and BBU


The digital Voice Phones connect to the DECT base station within the BT Smart Hub 2, not wifi.

The BBU in the ONT would not give any protection to the home hub in the event of a power cut, you would need purchase a separate BBU to keep the smart hub powered up.


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Message 3 of 6

Re: Digital Voice, Smart hub 2 and BBU

Thanks. This is what I initially believed it was just after reading the post I copied in it made it sound like it would power everything. And when on live chat to bt before ordering they claimed with the two phones they were supplying be and the bbu i already had i would still have a landline in the even of a outage. When the equipment turned up i couldnt quite see how it possible could. 

It does not bother me either way as we have not even had a landline for 3 years its just the fact i was told otherwise 

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Message 4 of 6

Re: Digital Voice, Smart hub 2 and BBU

Bear in mind that the latest ONTs no longer have battery backup, so are you sure that the one you have, has one installed?

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Message 5 of 6

Re: Digital Voice, Smart hub 2 and BBU

Yes definitely. I was surprised as its a new build only just completed and i read that all new instals wouldn’t have one from last year. Ours must be a older unit as it is branded BT Openreach and has the BBU installed. I Even took it ouch and checked there were batteries in it and turned the plug of so the power light on the modem went orange. They back on and the charging light came on

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Message 6 of 6

Re: Digital Voice, Smart hub 2 and BBU

Hi, I'm also being forced to take DV and have been sent a Smart Hub 2. I complained to BT that as the EE mobile signal is zero in my home and I must rely on WiFi calling so they sent me TWO BBUs (1 in error) intended for use with a Fibre Terminating Unit (as per the user guide in the BBU box). There is already an Openreach installed BBU connected to the FTU.

The BBUs they sent have a output power of 24W but the smart hub power adapter power output is only 18W. Does anyone know if this will be safe to connect to the Smart Hub? I don't want to damage it so not sure if I should connect it.


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