I have 3x SNZB 02D devices all purchased at the same time just over 6 weeks ago and have noticed a peculiarity with the battery indicator that has effected all three the same within within a few days of each other. The battery condition as reported on the device screen icon and iHost device card drops from 100% to 64%. The batteries removed from the devices measure 3.0 volts and on reinserting the same battery the display and iHost again report 100% battery capacity without it falling in value. All of the devices are in an area that has a temperature of around 23deg C. Has any other SNZB 02D user experienced this ? Thanks.
Yes. Some batteries and contacts cleaned then re-inserted. Created the following graph which shows which devices this was done on. Have just left them since, to see how long they last.
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Thanks for sharing your graph and I can see that 2 of your devices exhibited the same 100% > 60% drop in a short space of time as mine did. Iām using the original batteries that were supplied with the devices so will leave them to see what happens.
The CR2450 coin cells in some of my motion (Aqara P1) and temperature (SNZB-02P) sensors have been running for almost two years and are still functioning.
I recently measured the voltage of P1ās batteries, and it registered at 2,9V. When brand new, these cells typically show around 3,2ā3,3V, and they drop to 2,6ā2,7V when the sensors stop responding. This means the battery is currently at approximately 55% of its usable charge. In other words, after about 750 days of operation, only half of the battery capacity has been used. This P1 sensor operates in the kitchen, where movement is frequent, especially with my cat adding at night. It also reports illuminance. The detection interval is set to 60 seconds. So, after 6 weeks of usage, you shouldnāt notice any significant battery drain.
@Ramsdale makes a valid point about contacts. The air we breathe isnāt exactly pure, and when you factor in humidity, it further impacts the contacts, leading to voltage drops.
Doing a bit more testing Iām now convinced that the SNZB 02D has bugs in software version 2.3.0. for example
- In removing and replacing the battery it straight away shows a battery value of 18% remaining both on its screen icon and iHost.
- Same scenario but this time only the high few bars on the display icon, but iHost shows battery capacity as 100%
With the battery removed there is a residual voltage of a few millivolts at the device battery contacts that suggests itās internal capacitors remain charged.
For this device the temperature and humidity readings seem reliable but for the moment Iām going to ignore the battery condition indicator and rely on the iHost device activity log to make sure the temp and humidity are being updated regularly.
Youāre right. Thatās very likely. Letās hope that eWeLink guys take a closer look. But reporting battery levels is a weak point of almost every known to me Zigbee device. For example, TRADFRI open/close remote reports randomly various values (from 43% to 100%), although the cell was replaced a week ago for a quality one. And one thing more, end battery-powered devices are very ālazyā reporting this parameter. This we should bare in mind.
Re: the lazy battery reporting.
Iām using SNZB 02Dās in Home Assistant.
I take notice every few weeks to see if there has been a change in value.
I can then look at battery āHistoryā and see exactly when and what values have been reported.
For interest, I add them manually into a spreadsheet, which is where the earlier graph was produced from.
What would be nice then is, if the battery voltage was actually measured with a DVM each time. But that is not possible without removing each battery and that may have a number of consequences:-
Would the indicated battery level return to 100% again?
Or maybe some higher value than was just being indicated.
And:
Is this because the contacts have been disturbed?
Is it because the heat transfered from handling has had some effect on the battery?
Is it triggering / resetting something in the device measurement cct?
Software bug?
It would also risk loosing the device connection to Home Assistant and re-connection to HA is not something I want to have to do often.
It is interesting that the humidity peaks in the bathroom can be seen when a shower is used. Also in bedrooms overnight, by people simply breathing. It doesnāt happen if a room is not occupied or the door is left open.
But thatās a bit off topic.
Thanks and the observation about the humidity rising in the Bathroom while having a shower-- I use SNZB 02 (the device without the display) in the one of our bathrooms to trigger a switch that controls the extractor fan in there to operate when the humidity rises above the preset level. Iāve stuck with Sonoff scenes for all of my automation. Iāve made a length of foil insulated for most of itās length with clear sticky tape but uninsulated at each end so that one end sits between the battery and its centre connector- with that I can measure the battery voltage accuratly with the device operating. I can see that there are several issues posted in this forum about software problems with this device. Will keep an eye on what happens and keep the forum updated.
I just setup the same for my bathroom fan with a SNZB 02D and a ZBMINIR2. Works very well with a smart scene triggering the fan at 65%. I tested two 02D and two 02 devices in the bathroom for a couple of weeks before I set it up and the 02 devices were reading circa 15% higher on humidity than the 02D.
I have similar battery issues with the SNZB 02D. The one in the garage seems to eat batteries but now Iāve read this I expect Iām seeing the same issue. Please post your findings Alan.
I like Alans idea of using foil and sticky tape.
I wish Iād have thought of that a long time ago.
I did try powering one SNZB 02D located outside with two AAA batteries. That device kept dropping off the network every few days and I wondered if it was power related causing poor signal. (Involved soldering small wires to the contacts in the module).
However, It made no difference to it dropping off the network.
I should have thought about the foil strips idea then. Iāll try and add them and then get voltage data.
I also had three of these sensors, it is true they chew batteries. I now use ThirdReality Door Sensors that are better with battery consumption
Taking DVM readings of the battery voltage with the the SNZB -02D as the load (using the foil strip method detailed in my earlier post) I found: Initial insertion of Battery - Voltage 3.01 v, the device display (*see below) and iHost Card for the device show capacity as 100% after a few hours the Voltage measured was 2.99 volts, the device battery icon was just an empty rectangle and the iHost Card for the device showed capacity as 18%. Took the battery out, removed my foil āsensorā, reinserted the same battery and immediately the device and iHost display showed 100% again.
"during the tests the battery indicator on the device would only display the 3 bars in the right hand side of the rectangle for 100% capacity and the paired/ connected icon was not displayed at all although iHost was receiving Temperature and Humidity information throughout.
I was able to forget and re- pair the device several times without any problems but it didnāt resolve the display issues mentioned in * above, which just eventually corrected all by itself.
I also note that the SNZB 02D manual states that to change the display from the default DegC to DegF the button has to be pressed twice. What I found was that they have to be in rapid succession and any number of multiple presses 2, 3,4ā¦ will change the temperature format.
In conclusion I believe that these devices have a number of software issues. For the question of remaining battery capacity I would ignore the % shown and only change the battery if the device stops sending temperature and humidity information to what it is paired with.
For my outside sensor I use a Sonoff TH10 with the plug in temperature sensor. Itās a mains powered Wi-Fi device and 2.5mm 4 pole TRS Male > Female extension cables are available for it. Fortunatly one of my rooms has a ventilation duct to the outside so Iāve placed the sensor just inside of the exterior grille. Although TH10 is a switch device I use it to conrol a Sonoff Basic Wi-Fi switch adjacent to the boiler ā I have modified the Basic Switch to have clean relay contacts. If the external temperature rises above the preset value the Boiler will not fire despite whatever the internal thermosats (Sonoff TRVZB radiator valves) may call for heat. This arrangement has proved to be very reliable. Some time ago I did read a post which I think that you wrote about using a SNZB 02 outside. I also had tried the same thing and found when the weather got cold the battery condition depleted rapidly. I was going to go down a similiar route to yours but wire the SNZB 02 to a 3v DC mains adapter, but after reading your post I didnāt do that.
The new Sonoff zigbee door sensors have great battery life. In.my opinion.they will be even better if they had holes for screws. Adhesive tape is great but gives little options for relocations and repositioning of the sensors.
If the adhesive tape is the twin sided sticky foam tape, I came up with a useful solution for being able to move devices so attached.
My original use was for holding a childs stair gate open, located in a doorway, when it wasnāt necessary to have the gate closed. (They automatically swing shut if not held somehow).
I decided to attach a short piece of string using a cable-tie pad, to the back of the door to hold the gate open, if it wasnāt required to be shut.
I used a strip of pvc electrical insulating tape on the door, where the cable-tie pad is to be attached. Then stick the pad on to the pvc tape.
The tapes adhesive strength is really high when being pulled on directly, (at 90 degrees) but unlike the foam stuff, is easily peeled from an edge or corner, if needing to move it, without damaging the paintwork. Use fresh tape and another pad if it is moved.
(White door, white tape!).
But it should work equally well with door sensors or anything that uses twinstick foam for attachment.
For anyone interested in the child gate arrangement, use a magnet on the other end of the string to attach to the gate. (Assuming it is of steel construction). Then, if the door is closed and the gate closes (and locks), when the door is re-opened, the magnet will detach from the gate, to allow the door to be opened without breaking anything. The gate can then be used as normal.
Some of the battery levels on the SNZB-02Ds have dropped since posting values at the beginning of last month.
One has been indicating 0% for 5 days now, but is still working fineā¦
Zigbee end devices and misleading battery reports are a surprisingly common headache in smart home setups. Why battery levels can be inaccurate?
- Device firmware limitations: Many Zigbee devices estimate battery percentage based on voltage, which isnāt always linear or reliable. Some use Zigbee cluster 0x20 (voltage) instead of 0x21 (percentage), leading to guesswork by the device handler.
- Manufacturer differences: Accuracy depends heavily on how the manufacturer implements battery reporting. Some devices report 100% for months, even when the battery is clearly draining.
- Environmental factors: Temperature can skew readings. For example, sensors in cold environments may show lower battery levels than they actually have.
- Reporting intervals: Battery status is often sent on a fixed schedule, not in real time. This can delay updates or cause stale readings.
What you can do about it?
- Ignore initial readings: New devices might show 60% or 100% for weeks. Wait until the battery dies once to understand its real behavior.
- Use a voltmeter: For critical devices, manually checking battery voltage can give you a more accurate picture.
- Automate alerts: Set up automations to notify you when battery drops below a threshold (e.g., 10%), but donāt panic if it stays at 16% for months.
- Check for firmware updates: Some devices may improve reporting accuracy with updated firmware.
While platforms like eWeLink are making improvements with centralized dashboards and manual overrides, users may still experience false battery readings, dropouts, or delayed updates. For a reliable smart home experience, a mix of user vigilance and occasional manual checks are essential.
But donāt despair. Youāre not alone. Every smart home enthusiast has wrestled with the problem. Itās part of the chaos and charm of automation life. 
Thanks- very useful.
Update:-
Well, TH07 finally became unavailableā¦
One of my SNZB-02D devices had been reporting a 0% battery level in HA, for over 3.5 months.
HA finally reported, āUnavailableā, after 111days from first showing the battery level had dropped to 0%.
The battery removed measured 2.4V and the physical display was flickering.
TH06 battery was replaced after around 10 months operation. The other units are indicating various stages of battery level, but are still operating over nearly 12 months, as can be seen on the graph.
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Dame problem and I have already replaced the batteries and the situation has repeated itself. The batteries I took out have 3.3 volts so they are fully charged.
Exactly! I donāt know why Sonoff dis not add the screws option. Imagine the day you want to replace the batteries and the setup for is already glued one metre and a half above the ground