I thought I’d pop this up. It’s mostly common sense, but it took me a while to reach a rather basic conclusion:
When a device is updating lots, you want a larger, cheaper battery.
When it’s updating less often, you can get away with a smaller device.
Previously, all the zigbee sensors I bought were coin cell. Nice and small, comes with the battery, works straight away.
The first was a magnetic window sensor. Tiny device, and 2 years later, still running on the battery it came with. It only transmits when there is a state change, efficient, good plan.
Next up, a fleet of Sonoff ZB02 temperature sensors.
Tiny things, easy to hide around.
They update every few minutes.
After a year or so, the batteries started to go. 2032 cells aren’t exactly cheap, so I bought the budget brand, paying about 50p/cell.
However, the replacement cells last about 6 months.
Better quality cells cost about £1, and last a year.
This isn’t ideal, as they’re a bit of a pain to prise open, and not exactly cheap. Since I’d seen people online discussing modifications to add AA/AAA support, I thought I’d compare the capacity.
A 2032 generally has between 100 and 400MAh, depending on the brand.
An AAA has around 1000MAh.
And two are required to reach the 3v of a coin cell.
Depending on the quality of the button cell being replaced, that’s 3-10x the capacity. Price wise, it’s the same for me, £1 for two decent AAAs.
So based on that, I switched things up. Tuya sell sensors that run on AAAs.
And so far, the new temperature sensors are lasting much better.
They’re a little larger, granted, but it’s a good trade off.
Of course, I didn’t reflect about what I’d learned, and bought some new window sensors that take AAAs. It was only after setting them up, that I realised they’re big, and that the batteries will last until the heat death of the universe. Oh well.
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FYI, the only way to double the capacity using multiple batteries is to run them in parallel. You are running them in series (to double the voltage), so the overall capacity remains the same, in this case 1000mAh.
You’re right, I should have considered that. Thanks. Edit: Edited.
I was surprised by this, but if you care about the environment and need some coin cell sensors (or simply already have them) there actually exist rechargable coin batteries.
All rechargable batteries have MUCH lower energy densities. An ML2032 has literally 65mAh capacity. That would be maybe 4-5 months between charging all of them for OP’s temp sensors.
Much better to get rechargable AAAs. Eneloop AA/AAA plus a charger and you have many years of functional batteries with decent capacities.
I have several Shelley H&T sensors around the house which take CR123A camera batteries.
These are wifi, rather than zigbee, so the battery life on them is relatively short. I did something similar and bought cheap ones, only to find they have low capacity and lasted just a few weeks in some cases.
It took a while, but I found LiPo batteries which have (almost) the same physical dimensions, but higher capacity and are obviously better than throwing alkaline batteries away.
Yes, I’d go for zigbee in the future, but until I can justify replacing them, then this is the next best thing.
The only problem I have is catching the batteries dying in HA to tell me to replace them… the voltage drops a little and then either flatlines or returns to 100%… neither are something I can reliably trigger on… but that’s an automation challenge for another day.
Can’t remember the name at the moment but I had a HACS plugin that would pick up at the power level/battery sensors and warn you when they were below a threshold or offline for a specified amount of time
Ok, let me know if / when you remember - searching HACS seems to be dominated by integrations for SolarPV / offgrid batteries…
My home-grown solution should warn me when a battery is below x% - it’s just that rechargable batteries die quickly and the sensors can’t react… really I need to see if temp & humidity have flat-lined and warn on that…?
Respond to the battery level and if a device goes offline
Ah, thank you for the info, much appreciated!
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I’ve been using those AAA tuya sensors for a while now, with some rechargeable batteries they seem much less wasteful and last ages.
Not to mention that AA/AAA cells don’t use lithium so are slightly less environmentally disastrous
FWIW, I bought my first Aqara temperature & humidity sensors 4 years ago, and I only changed the battery twice despite getting cheap bulk Varta (0.7-0.8€ each) from Amazon.
For the Tuya stuff, is there anything special you needed to do in other to get them working with HASS? Most pages seem to indicate you need Tuya’s hub, which seems off
For me, I just turned them on, pressed the button for 5 seconds, and added them to ZHA.
I’m pretty sure Tuya are just keen to get people in their ecosystem/potentially avoid having to give tech support for HASS. And I honestly don’t begrudge them for that.
It should be possible to connect all Zigbee devices to another radio. From there, it’s just software integration, which for popular devices/chipsets is generally very good.
Did you actually save any money, buying new sensors for £8-10 each so you don’t have to replace a battery once a year for £1.
I think the point is that now he doesn’t have to take the time to go around the house prying the batteries out and replacing them every year. A small chore to be sure, but one that I’d be happy to do any with.
That, and I haven’t actually got up to replacement yet, as there were rooms that didn’t have a sensor.
I think I’ll experiment with adding an AA/AAA battery holder to the ZB02 next. If that ends up being too much of a faff, I might just sell them off cheap, and use the money to change to AAA sensors.ok, but it’s still once a year and unless it’s a castle with 43 rooms it can’t be that much of a hassle 😀
