Stop it with the coin cells!

Hey companies making sensors and remotes!

(for smart home/home automation and the likes).

If you can make a sensor microscopic – fine

If it needs to be portable – fine

But if it is rather small, but still visible you are not doing anyone any favor by making it as small as possible with a coin cell battery that runs just a few months or even less.

If your sensor can run for years and years on a pair of AA batteries, by all means use these! I want either a microscopic sensor – so small that i don’t see it or one with a battery that lasts forever.

The middle ground is crap. It’s still big enough that i see it and bothers me and has short enough battery life that bothers me.

Why would i want to have a slightly smaller sensor with much much less battery life? Do you think i like having 50 sensors/remotes etc with 6 months of battery life in my house such that every few days something stops working because of a low battery? Of course i don’t!

Plenty of devices are touting around ultra low power. Great! but it needs the other half of the ying-yang: ultra long battery life.

Why coin cell batteries suck:

-they have small capacity: a CR2032 has 14 times less than a pair of AA cells

-they are small and difficult to handle for many people, especially if you need screwdrivers pried in small indentations to open the box

-they exist in sooooooo many variants and many are used in sensors

-they are hard to obtain: the local supermarket has them for even 5 euros a piece

-they are more expensive per capacity: best case a CR2032 cost as much as one AA

So don’t use them unless the thing that uses it has to be as small as possible because it is portable or has to fit in some place. Otherwise, go for AA all the way! So:

Stop using coin cells in non portable sensors!

Example 1: Window or door sensor

This sensor can sense if a window or door is open or close. On the left: a commercial sensor operating on a CR2032 coin cell. On the right: my diy sensor running on 2xAAA for 5 times more battery life. Both are in the size region where they will be visible on the door/window frame but are not intrusive. The one with the bigger battery is way more comfortable to use, since its battery has to be replaced 5 times less often.

Dimensions on the chart are cm btw. 

Example 2: Motion sensor

Left: commercial motion sensor with a CR2450 battery. Right: my diy multi sensor module which covers motion, temperature, humidity, pressure and light level and which is running on a pair of AA batteries which will last 5 times longer than the one on the left.

Both sensors are sufficiently large to be observed, but not large enough to be intrusive. The one on the right with the bigger battery is far more comfortable to use, since it requires the battery to be replaced 5 times less often.

Example 3: remotes

Left: commercial 5 button remote from ikea running on a CR2032 battery. Middle: the same remote control has been optimized for running on a pair of AAA batteries, lasting 5 times longer. Right: a diy remote control with three buttons which also runs on AAA batteries.

Conclusions: use AA or AAA batteries

The sensor or remote control nodes will be barely any bigger than the ones with coin cells and will be far more comfortable for the user who will be disrupted far less often to replace the batteries.


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  1. Flux-Sucking Shunt

    Unfortunately the vast majority of buyers of these products (aka “consumers”) don’t realize this is an issue so I don’t think there is much pressure on vendors. They like tiny little sensors and will blame the batteries. I’ve seen it on the Simplisafe forums when the 3rd-gen system went to tiny batteries in the door/window sensors.

    Takes some work, but I have found white external covered battery holders for those sensors that just must have more battery capacity. That was before 3d printing became practical. Now I would just print a custom enclosure. All, of course, after exhausting the search for sensors with bigger batteries, and asking the companies if they have them and why not if they don’t.

    • Indeed, i have a few simple temperature / humidity devices that were hacked to work with AA instead of coincells. I think i never replaced batteries since them.
      You are right about the control being with the manufacturer. But maybe some manufacturers read complaints and improve the products.

  2. I like the a half AA or A123 3V batteries. They are powerful. Usually some the companies give the products with this type batteries 10 years working time.
    Try it – A123, CR17345, a half size AA. This is some othe names. They have 10 years shelf life.

    • CR123A is something that can also be good. However, they are rather expensive, even online in large quantities the good ones are about 3 euros or 5X more than a pair of AA. So a pair of AAA is far more comfortable to have. So i don’t see them as good for sensors that have this battery replaced. But, because of low leakage, they are common with water/heat/gas meters where the battery is supposed to last 10 years, the whole life of the meter and not be replaced.

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