Registering a new cordless handset

Page 26 says you can register 6 handsets. It sounds like there are handsets already registered. De-registering is on the same page.

https://panasonic.ca/viewing/ALL/KX-TG6431/OI/TG6431_PNQX1624YA/TG6431_PNQX1624YA.pdf

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http://www.panasonic.ae/EN/Manuals/KX-TG6541.pdf page 48 explains registering a new handset to the base unit

This solution is for the KX-TG2356 cordless phone
The problem you are having is not that the handset is de-registering but your handset is losing the link to the main base.You said you went through 6 handsets then, the only remaining thing that could cause your problem is: A bad handset battery. This would give you all types of connection problems and the Main base.
I will begin with replacing the battery. If that does not solve your problem then the problem would be the main base

I had this problem, and I fixed it by re-registering the phone to the base. Here are the directions for how to do that from the manual:


----->

Registering a handset to the
base unit
The supplied handset and base unit are
pre-registered. If for some reason the
handset is not registered to the base
unit, re-register the handset.
1 Handset:
{MENU}
2 {V}/{^}: "Initial setting"
{OK}
3 {V}/{^}: "Registration"
{OK}
4 {V}/{^}: "HS registration"
{OK}
5 Base unit:
- KX-TG4011 series:
Press and hold {LOCATOR} for
about 5 seconds. (No registration
tone)
- KX-TG4021/KX-TG4071 series:
Press and hold {LOCATOR} for

about 5 seconds until the
registration tone sounds.
If all registered handsets start
ringing, press the same button to
stop. Then repeat this step.
The next step must be completed
within 90 seconds.
6 Handset:
Press {OK}, then wait until a long
beep sounds.
Note:
While registering, "Base in
registering mode" is displayed on
all registered handsets.
When you purchase an additional
handset, refer to the additional
handset's installation manual for
registration.
<-----

See http://service.us.panasonic.com/OPERMANPDF/KXTG4011-MUL.PDF (page 22)

Try re-registering handsets to base unit, info on registering should be in manual.

You just got the manual for the handset. What you want is the one for the base unit. http://service.us.panasonic.com/OPERMANPDF/KXTG1032.pdf

you cant ..dont try ,,coz it have integrating problem in Panasonic Cordless Phone KX-TG1811AL ..hence contact coustmer care.,./,

The solution is this - unplug the base unit then plug it back in. After that it worked fine.

I've repaired thousands of these kx-tga400b phones and we have the only improved keypad that eliminates the common keypad problems for good.

Does the cordless phone have a 3 in the top right corner after it registers to 3? If so, then it is registering correctly. If it THEN consistently says "invalid, please register" there is definitely a problem with the main circuit board and it's not at all common. I've seen a few of these but it's a rare problem. We can fix it but I'm not sure how much luck you would have with any other repair facilities.

If you have the problem intermittently it's probably a bad RF module. That's a much more common issue.

If you are still looking for an answer on dereg of a handset, the manual says Menu - 0-0-2 then 3-3-5-OK then select the handset you want to cancel/deregister