Chapter in this post:
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.
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.
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.
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 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.
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.
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 .
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 .
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.
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.
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 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:
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.
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Jens has been running the blog since 2012. He appears as Sir Apfelot for his readers and helps them with problems of a technical nature. In his free time he drives electric unicycles, takes photos (preferably with his iPhone, of course), climbs around in the Hessian mountains or hikes with the family. His articles deal with Apple products, news from the world of drones or solutions for current bugs.