NiZn and lithium batteries as a battery replacement for Eve Thermo and tado thermostats

NiZn battery in Eve thermo thermostat

I tried mine some time ago Eve Thermo heating thermostats to operate with rechargeable batteries. Unfortunately, the app then constantly reports that the battery in the device is empty and in some cases it does not accept the batteries at all and you get no further in the setup process of the app. Without switching to batteries here, nothing worked.

The same game is probably known to users of tado radiator thermostats, because these also report with NiMh batteries that the inserted "battery" is empty.

Radiator thermostats from tado require 3 AAA batteries, but can just as easily be operated with rechargeable batteries - if you choose the right rechargeable batteries (Photo: tado).

Radiator thermostats from tado require 2 AA batteries, but can just as easily be operated with rechargeable batteries - if you choose the right rechargeable batteries (Photo: tado).

Update: Lithium batteries are the best choice

While I was writing the article, I came across a better alternative to NiZn batteries, namely lithium batteries. The electronics built into the batteries prevent deep discharge, which permanently damages many NiZn batteries. In addition, they have about 1200 charging cycles, while the NiZn batteries only manage about 500 charging cycles.

For these reasons, my recommendation is that you get lithium batteries. In order to save you the long reading of the article, you will find the right batteries for Eve Thermo and tado thermostats here, whereby I chose the cheap and well-rated variant with EBL:

A battery charger is not required for the lithium batteries, as they can be charged with a micro USB cable on a standard USB power supply unit. With the supplied charging cable, you can charge all 4 batteries at the same time on a USB-A port. The charging time is approx. Two hours.

If you are still interested in the background of my battery selection and a few technical information about lithium and NiZn batteries, you can now read on.

Note from my reader Wolf:

Lithium batteries are good, but they have one disadvantage: they deliver a constant 1,5 V. The cell voltage of 3,7 V drops slightly. And the battery suddenly switches from 1,5 V to 0 V. The thermostat cannot tell whether the battery is empty. And overnight the thermostat switches off in the last position - if you are unlucky, it is just at 0%. Or 100%.

The problem is actually also with the NiZn batteries, because they are reported quite abruptly as empty and stop working. The disadvantage is that the NiZn batteries are then deeply discharged and often break. This no longer happens with lithium batteries.

Update 03.02.2021/2/2019: tado VXNUMX from XNUMX will recognize batteries

In the support area of ​​tado I was just able to read that the newer devices (V2, which will be on sale from 2019) also recognize NiMH batteries from eneloop and adjust the battery warning accordingly. Here is the note from the side:

To what extent the devices can also handle other NiMH batteries, I cannot say, but eneloop batteries are just simple NiMH battery types.

 

Despite the completely fresh battery, the Eve app says that the battery is empty - we want to change that.

Despite the completely fresh battery, the Eve app says that the battery is empty - we want to change that.

NiMH rechargeable batteries as a battery replacement only possible to a limited extent

Now, of course, one wonders why the device thinks that the battery is empty when the battery is fresh. The reason for this lies in the different voltages used by alkaline or zinc-carbon batteries and nickel-metal hydride batteries.

While alkaline and zinc-carbon batteries have a cell voltage of 1,5 volts, nickel-metal hydride batteries only achieve 1,2 volts per cell. The electronics in the Eve Thermo or in the Tado thermostat therefore consider the battery to be a fairly empty battery and report this in the app.

One way would be that you could simply say in the Eve app that you have a NiMh battery in it, so that the lower voltage is correctly interpreted. However, the programmers have not yet implemented this, so you have to take a different path.

The nickel-zinc batteries (NiZn) seemed to me to be the best choice ... until I found out the disadvantages (photos: Sir Apfelot).

The nickel-zinc batteries (NiZn) seemed to me to be the best choice ... until I found out the disadvantages (photos: Sir Apfelot).

Nickel-zinc batteries as a battery alternative

The second - more elegant - way is to switch to a different battery technology - namely to NiZn batteries. These nickel-zinc accumulators have a cell voltage of 1,6 volts and are therefore not recognized as an empty battery, but act on the electronics like a very well-filled battery.

Stable discharge curve: a curse and a blessing at the same time

They also have a very constant voltage curve during discharge and only lose a massive amount of voltage when they are really empty. Basically this is an advantage, because the supplied devices have a constant performance for a very long time.

However, this creates the following disadvantage: The electronics in the Eve Thermo consider the battery to be full even when it is almost empty. This means that you will only be warned that the charge of the battery is on "reserve" when it is actually already empty. If you do not take care of the replacement and charging immediately, you run the risk of the battery being deeply discharged and damaged as a result.

Here you can see the discharge curve of NiZn batteries in blue compared to the red curve of NiMH batteries. NiCd actually no longer play a role, as they are banned in trade (graphic: Wikipedia).

Here you can see the discharge curve of NiZn batteries in blue compared to the red curve of NiMH batteries. NiCd actually no longer play a role, as they are banned in trade (graphic: Wikipedia).

Set up calendar entry for exchange

To prevent the batteries from being deeply discharged and thus permanently losing a large part of their capacity, I always make a calendar entry for 2 to 3 months and then walk around the house to charge all Eve Thermo batteries and equip the devices again .

Which NiZn batteries should I use?

If you look around on Amazon for NiZn batteries, you will quickly notice that you will find very mixed reviews and that there is virtually no manufacturer whose NiZn batteries only have 4 or 5 stars. Why is this so?

It's simple: People use NiZn batteries in devices that are designed for batteries or NiMH batteries. The result is that the message "Battery weak" in the devices comes much too late and the voltage of the NiZn batteries has already reached such a low value due to the strong discharge that the cell is permanently damaged because it has been discharged too far .

I use Ansmann's NiZn batteries, but would now use lithium batteries. Why? I'll explain that in a moment ...

I use Ansmann's NiZn batteries, but would now use lithium batteries. Why? I'll explain that in a moment ...

Bad product reviews due to misuse

All the Amazon customers, who are screaming that the batteries hardly have any capacity after a short time, have probably killed them themselves by removing the batteries from the devices too late and plugging them into the charger.

So my recommendation is: It's better to change and charge the batteries too early than too late. A recurring reminder under macOS or iOS can be created quickly and may save one or the other battery.

For this reason you can use all NiZn batteries equally, because the ratings simply say nothing.

My attempts with NiMH batteries were unfortunately not available because the nominal voltage of the cells is too low (Photos: Sir Apfelot).

My attempts with NiMH batteries unfortunately failed because the nominal voltage of the cells is too low (Photos: Sir Apfelot).

List of NiZn batteries for the Eve Thermo and tado thermostats

Here is a list of NiZn batteries of the size AA, as they fit into the Eve Thermo and tado thermostats. Please consider: you need two batteries per device.

I have the Ansmann batteries and I am quite happy with them. I have to admit, however, that I have already crushed some of them because I loaded them too late.

Best (!) Alternative with deep discharge protection: lithium batteries

Actually, it is almost a bit of a shame that I only discovered these batteries when the article was almost finished, because ultimately this type of battery is the best solution, as they have built-in protection against deep discharge - one thing that many NiZn batteries do saved life.

But now to these great things: There are lithium batteries that actually have a cell voltage of 3,7 volts. However, built-in electronics reduce the voltage to the 1,5 volts that we need to replace batteries.

It should be noted here that this type of battery is not filled with conventional chargers, but rather via the supplied USB cable with four micro-USB outputs that are plugged directly into the batteries.

The charging cable with the four micro USB plugs is included. Everyone should already have a USB power supply at home (Photo: Amazon).

The charging cable with the four micro USB plugs is included. Everyone should already have a USB power supply at home (Photo: Amazon).

The advantage of the deep discharge protection and the built-in charging electronics is bought at a slightly higher price and less capacity, since the electronics naturally cost money and also require space. Nevertheless, the investment seems more sensible to me than having to buy new NiZn batteries every few months because they had been forgotten.

Here is a short selection of the products for you:

Lithium batteries (AA) for Eve Thermo and tado

I hope I was able to help you a little with these tips when converting the tado and Eve Thermo devices. Of course, the mentioned battery types also work with all other devices that insist on batteries and do not want conventional batteries: flashlights, remote-controlled cars, remote controls and many more.

I would be happy if you write me in the comments where you use or want to use these batteries.

-
 

8 comments

  1. Florian says:

    Hi Jens,
    the Tado radiator thermostat uses 2x AA instead of 4x AAA.
    As far as I know, the room thermostat needs 3x AAA. But I'm not sure because I only have the one for the radiator.
    Greetings Florian

    • Jens Kleinholz says:

      Hello Florian! Thank you for your hint. I don't use a tado and actually made a mistake in the device on the support page. You're right with 2x AA. The newer models also seem to recognize eneloop batteries and accept them. I'll rewrite that in the article.

  2. Wolf says:

    My Eve thermostats were fed with Eneloops the first time the battery was changed.
    Eneloops are the best NiMH batteries. Not the ones with the greatest capacity, but those with the lowest self-discharge. Can also be used 1 year after the last charge. Other NiMH are already empty. This is one of the reasons why they are used as a standard by professional photographers.

    Lithium batteries are good, but they have one disadvantage: they deliver a constant 1,5 V. The cell voltage of 3,7 V drops slightly. And the battery suddenly switches from 1,5 V to 0 V. The thermostat cannot tell whether the battery is empty. And overnight the thermostat switches off in the last position - if you are unlucky, it is just at 0%. Or to 100%

    • Jens Kleinholz says:

      Hello wolf! Thank you for your hint. I add that again with the lithium batteries. I also have Eneloops, but my Eve Thermo doesn't like them. Do you have the new version of Eve Thermo, where you can set the temperature yourself on the Eve Thermo? I still have the old version, where everything is only possible via Home or Siri. Maybe you have built in a battery detection in the newer version, like tado? Also, and most of the time the thermostat is not set to 0 or 100%, but somewhere in between. It only readjusts very finely when I look at the curve. But of course ... it could be that the room is cooler or warmer than it should be.

  3. peter v. says:

    Interesting tech approach. Unfortunately, I just ordered and received AA-size lithium batteries 3 days before via an instagram advertisement. Just have their own charger, which can also charge NiMh.

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