This topic

Battery Backup for Broadband / Digital Voice - Not working (?)

Bilgepump — Sun, 18 Oct 2026 12:59:58 GMT

Our battery back up doesn't work. As far as I can tell, it is correctly set up. The battery is fully charged and connected to the Hub. However, when had a localised power cut yesterday (our house only), neither the broadband nor the digital voice worked. This kit cost £80 and doesn't work. Can anyone help or advise? Thank You.

Re: Battery Backup for Broadband / Digital Voice - Not working (?)

iniltous — Sun, 18 Oct 2026 13:23:40 GMT

Clearly if the broadband router wasn’t powered by the BBU during a power outage then DV can’t work either , assuming you are on FTTC and not FTTP ( in which case the ONT would also need its power maintained during a power cut ) the evidence would suggest your router isn’t connected to the BBU correctly or is faulty.

Re: Battery Backup for Broadband / Digital Voice - Not working (?)

Bilgepump — Sun, 18 Oct 2026 13:53:04 GMT

Thanks for your reply, Iniltous. Yes, we're on FTTC. The BBU was connected and the router was lit, but purple/magenta, not blue. The BT backup only has two ports - one for power in and the other for a data connection to one of the four ports on the hub. It looks increasingly likely that the BBU I paid BT £80 for is not fit for purpose. Any advice you can give would be gratefully received. Thanks.

Re: Battery Backup for Broadband / Digital Voice - Not working (?)

licquorice — Sun, 18 Oct 2026 14:20:01 GMT

If the router was lit the BBU was clearly working and powering the hub. If the hub was purple, it indicated a line fault. Possibly the cabinet had no power.

Re: Battery Backup for Broadband / Digital Voice - Not working (?)

iniltous — Sun, 18 Oct 2026 14:38:43 GMT

Presumably it’s quite easy to simulate a power outage , I’d assume the router is connected to the BBU (not directly to the mains ) and during a power outage the BBU which is connected to the mains , detects the mains failure and takes over supply to the router, so disconnecting the mains to the BBU imitates the mains going off …try this , does the router remain powered ? ,

Its possible if there is a short disconnect while the BBU switches to take over supply after a mains failure, the router will lose sync and have to reconnect, so it may not be a seamless transition to the BBU taking over , presumably you waited a while before deciding it wasn’t working rather than checking the second the mains went off and assumed the router wouldn’t reconnect ( as stated it clearly was getting some power if the LED was illuminated.

Try simulating a clean mains fail and observe what happens , if your local mains issue wasn’t a simple mains off , and then come back on later , but a more chaotic disconnect , this may have messed up the re syncing of the router

Re: Battery Backup for Broadband / Digital Voice - Not working (?)

licquorice — Sun, 18 Oct 2026 14:35:46 GMT

The BBU is obviously working or the hub wouldn't be lit.

@Bilgepump the BBU only provides power, it doesn't guarantee a broadband connection.

Re: Battery Backup for Broadband / Digital Voice - Not working (?)

Bilgepump — Sun, 18 Oct 2026 15:02:35 GMT

Thanks, Liquorice, for your reply. This was therefore missold to me by BT as the means to ensure that our phone would still be useable for at least an hour in the event of a power cut. Does this mean that I can return it for a refund of the £80 cost?

Re: Battery Backup for Broadband / Digital Voice - Not working (?)

Bilgepump — Sun, 18 Oct 2026 15:04:43 GMT

It all came straight back up as soon as the offending extension lead was replaced.

Re: Battery Backup for Broadband / Digital Voice - Not working (?)

licquorice — Sun, 18 Oct 2026 15:08:14 GMT

In most cases, it would be unlikely that the cabinet would lose power as it has battery backup capability, it is possible during an extended power outage the batteries would become.e depleted and the cabinet also lose power. This would be a rare occurrence.

The BBU is obviously sold to provide power to the router which it clearly does.

Re: Battery Backup for Broadband / Digital Voice - Not working (?)

Bilgepump — Sun, 18 Oct 2026 15:22:32 GMT

Clearly not to the OLTE, though, which renders it useless. 🙁

Re: Battery Backup for Broadband / Digital Voice - Not working (?)

WSH — Sun, 18 Oct 2026 15:29:19 GMT

What's an OLTE? If you mean the equipment to convert electrical signals to optical, that would be in the "exchange".

If you mean ONT, I thought you said you were on FTTC? Obviously, the ONT would also need battery backup.

Re: Battery Backup for Broadband / Digital Voice - Not working (?)

Bilgepump — Sun, 18 Oct 2026 15:58:15 GMT

Apologies, we are on fibre all the way, so FTTP. I'm a bit out of date with terminology, I'm afraid. OLTE used to mean Optical Line Terminating Equipment. So a second backup battery is needed?

Re: Battery Backup for Broadband / Digital Voice - Not working (?)

licquorice — Sun, 18 Oct 2026 16:01:46 GMT

Disregard all posts up to this point, based on incorrect information.

It should be obvious you need a BBU to supply both router and ONT.

Re: Battery Backup for Broadband / Digital Voice - Not working (?)

gg30340 — Sun, 18 Oct 2026 16:33:15 GMT

@Bilgepumpwrote:
Apologies, we are on fibre all the way, so FTTP. I'm a bit out of date with terminology, I'm afraid. OLTE used to mean Optical Line Terminating Equipment. So a second backup battery is needed?

Depending on the BBU that you have you have and where your equipment is sited in regards to each other you could just plug a double socket extension lead into the BBU and the ONT and BT Hub into that.

Obviously if you are using a BT BBU the above would not be relevant because there is no 3 pin socket to plug into.

Re: Battery Backup for Broadband / Digital Voice - Not working (?)

WSH — Sun, 18 Oct 2026 16:32:01 GMT

Well, that's what's got me confused. In message 8, the OP said "It all came straight back up as soon as the offending extension lead was replaced." What extension lead? Does he mean a splitter lead that came with the BBU? In which case, the plug for the ONT end may be the wrong size.

Re: Battery Backup for Broadband / Digital Voice - Not working (?)

iniltous — Sun, 18 Oct 2026 16:36:57 GMT

Asked specifically if they were FTTP or not , and giving the wrong answer suggests they probably have the wrong BBU , presumably they should have one of these assuming the ONT and router are close to each other
https://youtu.be/zYmlWR6NU-g?si=79dJAZACS7MV5Dad