NiMH batteries ok for the OR Battery backup?

Had cause to unplug my surge protector that my setup (including the ONT) is plugged into and when I switched the power back on, the charge fault light came up.

Power cycled again and it still came back so guess the original batteries are knackered (was installed in Jan 2018)

Going to get a pack of Duracell rechargeable AA batteries but can only get NiMH ones, will they be ok (I've not checked what type are in there at the moment)

Are these ok?

Yes they are Ni-MH. Unfortunately they simply fail in capacity badly after about 18 months, especially as they aren’t regularly fully discharge-charge cycled - which this particular chemistry needs to keep them fit.

Does the BBU power the whole ONT, or does it just power the voice port? A Google search gives results that argue both ways.

It powers the whole ONT; the voice port is just a part of the ONT. And without the rest of the ONT, it wouldn't be able to communicate over the fibre anyway.

Yep. As said the whole ONT. Never used the voice port. Get around 45 mins to 1 hour on a fresh set of batteries. Old Huawei 1+1.

In reply to a post by Pheasant:

Yes they are Ni-MH. Unfortunately they simply fail in capacity badly after about 18 months, especially as they aren’t regularly fully discharge-charge cycled - which this particular chemistry needs to keep them fit.

Modern ones are pretty good by all accounts, Big Clive done a video about them a couple of days ago., only afour-minute video

I have some old Tandy ones, and they do discharge, not too bad considering, I have some in the mouse I am using on this machine and they last for a few weeks. I think they must be way over ten years old.
I do need to buy some new ones as some of the ones I have got my charger says are bad.

In reply to a post by jpm:

Does the BBU power the whole ONT, or does it just power the voice port? A Google search gives results that argue both ways.

I don't know how it could possibly do anything other than power the whole ONT.
Does it not simply connect to the DC in power port?

The BBU port found on the original ONT's was simply a telemetry port used to tell the ONT if the batteries were dying/dead.

SIN 506 section 2.3.5 details what ONT's should be compatible with the Openreach BBU's. The newer 1+0 models may also work with a BBU.

The Battery Back Up units for the ONT's are pretty useless without also powering your router.
They only served a purpose for users who used voice via the ONT phone port (FVA) but that was withdrawn from sale nearly 2 years ago now. I believe only BT ever used FVA.

If someone is going to the effort of powering both ONT and router then it makes sense to use a UPS for both rather than a BBU + an alternative backup power supply for the router.

Edited by j0hn83 (Thu 30-Dec-21 00:24:27)

In reply to a post by Pheasant:

Yep. As said the whole ONT. Never used the voice port. Get around 45 mins to 1 hour on a fresh set of batteries. Old Huawei 1+1.

I lied 🤥

Pulled the plug from the wall (BBU with original batteries from 2019). The BBU stood up the ONT for just over 3 hours.

In reply to a post by Pheasant:

Yes they are Ni-MH. Unfortunately they simply fail in capacity badly after about 18 months, especially as they aren’t regularly fully discharge-charge cycled - which this particular chemistry needs to keep them fit.

Thanks for all the replies and all the best for the New Year to you all.

Changed them today, luckily I bought 2000 mAh ones as there's a warning notice on the inside of the battery compartment cover stating this is the minimum capacity that should be used.

As an observation before I replaced them the fault light had gone out and it eas showing Green again but thought it best to replace them anyway.

Edited by techguy (Sun 02-Jan-22 20:01:59)

You can use what capacity you like tbh. The stand up time will just be commensurately shorter or longer.

(Amazon had 4 packs of Duracell 2500 mAh AA’s for £9.35 on Prime)