Question about BT Voice, dropping sync

[wamdue]

Trying to sort my mothers BT Voice phone.

So first of all, despite all her claims about not hearing the phone, both of them (1 has had a battery change), can make and receive calls on demand. So its not a total failure of them.

However when I do things like press the voice mail button (top right), it either looses sync the Hub, or shuts down, and has to find its sync again.  This is also true, if I try to use speaker phone.

I cant pretend that these are issues which bigger than "user error", but they are errors I can not fix, or quite understand.

Internet itself, seems to be plenty stable and works without issue.

Any ideas?

[iniltous]

It not clear to me what you are asking , if on DV and using cordless phones , either a ‘free’ DV phone BT supplied or your own cordless phone , it’s not WiFi connectivity it’s DECT , so no different to any other cordless phone, in that regard DV is irrelevant ….if there is a voicemail button on the BT supplied DECT phone  , presumably all that does ( in effect ) is ‘dial’ 1571 to enter  the ‘voicemail’ menu, so it could be a range issue , basically too far away from the DECT base station ( the SH2 ) or the phone itself is faulty, or it’s range inferior to whatever was used previously.

If it is the ‘free’ BTDV phone or phones that are not working satisfactorily, presumably you still have the ( DECT cordless ) phones that were previously in use , they can be used , you don’t ‘need’ to use the BT supplied ones, simply connect the phones you had previously, if they were OK before DV , there is no reason why they won’t be OK now, albeit the base station may be in a different location ( as it would need to be connected to the SH2 ) 

[wamdue]

Yes it is the BT supplied phones.

No it is not a distance issue.

The previous hand sets have been gotten rid of, as we no longer have a land line.

[Keith_Beddoe]

@wamdue 

Just a note.

The old handset would have worked just as before, provided they were plugged into the phone socket on the back of the Smart Hub 2 instead of the socket on the wall.

[Thorn55]

We had the same thing with our DV Basic handsets: when a ringing phone is picked up it goes into its start up sequence (on our old phones it showed a BT logo, the new ones show a 'power on' symbol) then looks for the hub and re-syncs. The call, of course, is lost.
(See also https://community.bt.com/t5/Home-phone-including-Digital/Incoming-call-turns-handset-display-to-bt-l... and https://community.bt.com/t5/BT-Devices/voip-phone-stuck-on-synchronising-handset/m-p/2220534 )
It appears that when the batteries wear out,  trying to ring when 'off  base'  is too much for them, and the handset goes into its 'off' state and then re-boots.
Taking the battery out for a short rest may allow a small amount of recovery but basically it needs new batteries.
These are NiMH AAA cells. The manual says a label on the base tells you if you need  'type A' 800 mAh or 'type B' 850 mAh, but ours is inside the battery compartment.  To be honest I can't see why it would  matter so much- it's less than 7% difference in capacity. 
If you decide to test with ordinary alkaline AAA cells,  I suggest that you take them out afterwards- the base will try to re-charge them and things may get messy, also the voltage is 25% higher than the proper cells.
The charging system obviously has issues - our new DV handsets only lasted 9 months before needing new cells. The old BT6510's were still going after 9 years!