Battery doorbell will not charge when connected to 16v transformer

I am having trouble with my 2K battery doorbell. It is connected to a 16v transformer. The plug symbol shows up on the screen as if it is being charged/powered by the transformer, but the battery does not charge and dies. Could this be because of outdoor temperatures and lithium batteries not liking the cold or is there something wrong with the doorbell. It will charge from the home base when connected to it. It has been confirmed that 16volts is going to the doorbell. In fact I replaced the transformer to make sure that wasn’t the issue.


I have the same issue.

Several possible reasons this happens.

  1. Transformer current rating too low. Eufy requires 30 VA. You can have 16 VAC at the doorbell, but if the current rating is too low, you will show the plug icon, but gradually lose your charge becasue the doorbell doesn’t have enough current from the transformer. Transformer rating should be stamped on the side of the transformer. Also, if you are using the existing mechanical chime, it will limit current going to the doorbell

  2. Cold weather (below 0C) charging is not as efficient. Internal charge controller will cut back charge in colder weather to prevent damaging batteries. If your battery charge gets too low, in cold weather, its better to remove the doorbell and charge in a warm place than to count on the external charging.

  3. Also in the equation is the number of activations you are getting on the doorbell. Eufy has calculated electrical requirements based on 10 activations per day, at 68deg.F, and lasting 30 seconds per activation. If you are getting more, or longer activations, at colder temps, you will need more current to keep everything charged. Best way to know whats going on is insert a meter in series with your transformer and see how much its charging.

All these items can combine to cause problems. Best course is to check whatever you can one step at a time and try to isolate the main issue. A $20 multimeter can reduce the time troubleshooting a lot.

Not true. Think this must depend on the market area.

Here in the UK 8v 0.5amp is ample to keep them working and charged correctly

Wired needs 30 to 40av, battery only 8va.

Thanks for the info. It is a 30va transformer. I am suspecting the cold weather is the issue as that is when the issue began. We are supposed to start having warmer weather in my part of the states this coming week. I am going to see if that solves the issue.

when your wires are to thin for the distance the power on the doorbell can drop a lot. I use a 1 square mm wire for a distance of 6 meters. When the wires get hot replacement the wires because it can cause a fire.

Dont know what this is in inches.

@wij6 I don’t know where you got the information that the battery doorbell needs a smaller transformer. Since the battery doorbell supports a mechanical chime, and the wired doorbell does not, the battery doorbell should require a larger transformer just for that reason alone. The specs for the wired doorbell clearly show in the Help section of the app at 30VA. There aren’t any comparable specs in Help for the battery doorbell when powered by existing wires.

This board and Reddit are full of users that are complaining about their battery doorbells not keeping the batteries charged. Many of them are using existing 8VA transformers. I’ve done some measurements my doorbells and when the weather is warm and the number of activations low, you can get by with an 8VA transformer. However, when things cool off, or you have more activations, or use live view a lot, 8VA doesn’t cut it.

I had contact with support

Thank you so much for contacting eufy.
Usually, eufy 2k battery-power doorbell works with 8-24V 10VA or above.
You may refer to the following transformer.

Thank you again and have a great day!

because Daisy said 10va but linked to a 8va tranformer, I ask why the difference.

Daisy’s answer

Usually, 8VA is also ok. But it would be better to have 10VA. But I
didn’t find a 10VA transformer online, so I recommended a 8VA.
Thank you again and have a great day!

So you may be correct that 8va is not enough, Eufy is nog clear about 10va or 8va. The old-fashioned doorbell only uses power for the time you press the button, 1 or 2 secondes. My mechanical doorbell uses 8 volt and 0.08 ampere. That shouldn’t be a problem, I guess.
Tomorrow I will install the video doorbell and then I will see or maybe a few weeks later when the battery loses power.

Since I am starting the installation tomorrow I kept thinking about this, so I went through the help section of the eufy security app. This is what I found.

‘The battery doorbell (T8210) has a built-in 6500mAh battery. You can charge the battery doorbell with a 5V/2A, 5V/1A USB charger.
If using 5V 1A, it takes about 6 hours to charge from 0% to 100%.
If using 5V 2A, it takes about 3 hours.
P.S. The HomeBase 2 USB port can be a 5V/2A USB charging port.’

‘The wired doorbell (T8200)
Make sure the transformer for doorbell delivering 16-24V AC, 30VA of power.’

Charging on a usb port 5VA takes 6 hours. Why should 8VA not be enough from a transformer with good wiring?

It is not a good idea to force charge a Li-ion battery during a frost period.

‘Charging batteries and temperature
The temperature implications for battery charging are even greater.
To maximize the life of lithium-ion batteries, they should not be charged at temperatures below zero degrees celsius or with very low current only (trickle charge).
A conservative charging current is also necessary at low temperatures just above zero. Using the same scale as above, this is visualized in the chart below.’

If it is freezing, maybe charge it indoors?

So far it appears to be temperature related. I charged it indoors from the home base 2 and then reinstalled outdoors once the temp was back above freezing. We have been above freezing (32F) for the last 48 hrs and the doorbell appears to be staying charged without issue up to this point. I will keep everyone posted as the week goes on. We are supposed to go below freezing at night the second half of this week, we will see how it responds.

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Clearly, Eufy has built in protection against charging at temperatures below 40° F as it can damage the batteries.

After the installation 4 days ago it is now also clear to me that 8va does not work for me.
So #preset was right, 8VA is not enough.
Tuesday, Feb 23. battery doorbell installed, Saturday the 27th it became clear that 8va (8v 1a) is not working for me. The old doorbell stopped working and the eufy app indicated that the battery was being charged, but it stuck at 86% for 8 hours. Ordered another transformer (18VA), let you know how that works.

Outside temp is 8° celcius (46° F》