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.

  • SayCyberOnceMoreEnglish
    3·
    8 months ago

    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.