I had a S220 video doorbell connected for about 1.5 years then spotted battery low message. Removed and charged up battery but when connected back it was only showing battery power. This went down within 6 weeks and I recharged the unit twice. Eufy advised that it could be the hardware and offered a discount if I purchased a new doorbell .
I have now connected a new S220 video doorbell choosing hard wiring option but it also is only showing that it is using battery power.
I have checked the wiring with a multimeter and unloaded getting a reading of around 28.
Has anyone else had this issue as I did read previously that sometimes there were issues after firmware updates but Eufy are not confirming if this could be the issue and keep advising me to reset the unit and check the transformer and wiring circuit.
I really would appreciate any advice others can share as otherwise have been very happy with the unit - not so much now I have purchased a new one and still not resolving the problem 
You may have to replace the doorbell transformer. When my doorbell camera went to battery, I had to wire in a new transformer. Old one was 40 years old and hidden in the wall somewhere. It lasted nearly 3 more years powering the camera.
Strange if you followed instructions and you have power there it should work. You said you had 28 volts at the wires? 99% of the time a standard doorbell is only 16 volts so someone must have changed it out to a larger 24 volt one which is still alright but still doesn’t explain why it isn’t working?
Thanks for the input . The transformer was replaced when I got the Eufy doorbell initially and I think that when checking the wiring if it does not have any load on it the ready can be slightly over what you expect . Expecting 24 showing 28/29.
I have now received a message from Eufy : The T8210 S220 doorbell is a battery-powered doorbell; unlike the wired version, it cannot be converted to run solely on hardwired power. Even when connected to doorbell wiring, it does not function as a fully wired model.
If the battery is uncharged or removed, the device remains fully functional while hardwired; however, the hardwired connection does not transform it into a strictly wired-power version.
There is currently no information indicating that firmware updates cause the device to switch to battery power.
If a low battery warning appears, please verify that the power adapter meets the device’s specifications and check the wiring for any looseness, damage, or poor contact. You can also view the charging status in the app by navigating to “Side Menu > My Devices > Doorbell Name > Power Management.”
The device features a built-in, non-replaceable battery; the doorbell must be removed to recharge it.
This information does not help as I was under the impression that hard wiring would always allow a trickle charge to keep the battery level for far longer than the battery on its own.
Away to have a look at the comments regarding the same doorbell issue that others have had when a firm update was done - bell changed over from hard wiring to battery power
you are correct a 24 volt transformer will read higher without a load. I have the exact same door bell camera for almost 3 years and I have never had any issues with it but I didn’t realize that it wasn’t using the transformer to work but only to charge that is interesting. I do see in the app it charging every couple of days so I guess that makes sense. They do make ones that are just powered without a battery I have installed them for customers before
Thanks ele1980 as this confirms that i should be able to have the doorbell functioning for a long period of time without requiring a battery recharge. I am still going back and forward to Eufy customer services and will report back here when I get this issue resolved.
one response from Eufy advising they will send out a replacment once I send this one back and another reply advising their technical team looking into the problem - strangely both emails from the same adviser!
Did they also attach a return shipping label? If so they approved the return
No label received & have found out that as I sent an email out with the origina thread AI provided a separate response. I think this is the one accepting the unit back for a replacement!!!
Now have to wait 3 days for technical team to advise.
Will update here ……..
Perhaps a hard reset, and follow new setup instructions again.. Hope this helps 
Thanks for the suggestion. Yes tried resetting , removing & re attaching all devices.
I can’t get my head around why it won’t connect to hard wiring 
Hi, I’m not sure if that camera is using spring terminals within the doorbell. The hard wire screws when tighten contact them terminals.
The spring terminals may not just be springing / moving back out.
Completely remove the terminal hardwire screws from the rear of the doorbell, and gently insert something that will fit through the screw hole.
Check for resistance/slight tension of spring back.