...so the company making parts with them can then extoll the virtues of "biodegradable" in their marketing...?

Also, for those who doubt the claim about the Honeywell thermostat having a battery, I did some further research, and it does appear to be true:

https://forum.heatinghelp.com/discussion/128526/honeywell-th...

https://www.amazon.com/review/R3V5R0MJGEFNXH

But then this video shows that it is relatively easy to replace, it's not soldered in place, although the comments there do mention that the presence of the battery isn't documented anywhere in the original instructions:

https://www.youtube.com/watch?v=6VKowLXfERo

Many people add ficituous evidence of their views because they are so sure they are right.

Also, the gears inside of refrigerator defrost timers in the 160 refrigerators we bought for an apartment complex. Shockingly, still mechanical. And one of the gears is date coded and has teeth made of a rubbery, disintegrating plastic around a regular nylon wheel. The vast majority of the timers failed in a two years window. At 7-8 years. The cheap replacement timers have no such nonsense and I’ve never seen one fail. Most people just would have replaced the cheap apartment fridge.

This is just some of what I’ve personally seen.

But you are right, I’m just some guy on the internet, I could be just making this up.

And corporations would never make things with life limitations to make more money. Surely. I mean, that would be like a subscription model! Ridiculous!

If the latter, how does it help Honeywell that you have to replace it?

Since we had over a hundred of these deployed in an apartment complex, when they started failing I carefully characterized their behavior. It just makes them go wonky when it is removed or dies. The at328p functions fine without it, there is no RTC or anything that needs a battery., and the chip is not powered by the battery when power is removed. In fact, there is no discharge from the battery when power is off. The at328p has nonvolatile eeprom and flash storage.

Interestingly, the wonky behavior it exhibits is the same (but doesn’t go below 40 degrees (f) ) as an old electromechanical one failing lol.

This is exotic enough that replacements are very hard to find. I can either get the 2 cells needed from the manufacturer at about 70% the cost of a new light, or get a new light. It’s technically repairable/user serviceable, it’s just not practical to do. Apple is playing a similar trick with their 80lbs iPhone repair kit to change the battery yourself: technically user repairable, practically not.

Huh? You seem to be contradicting yourself: you say it's a standard 18650 cell. That's not something custom, that's something you can buy from an electronics supplier quite easily. And no, having both poles on the same end isn't something custom either, that's just a variant you can buy. You should be able to find this exact part on digikey.com.

>This is exotic enough that replacements are very hard to find.

If you can buy something on digikey.com, it's not "exotic". They even ship small orders by USPS for cheap. It might be "exotic" to a typical consumer, but those people don't know how to use a soldering iron.

We all know the typical HN reader thinks a fun weekend would be spending 6 hours researching part numbers and getting out the soldering iron, but we are atypical. Most people will assume their product is at the end of its life because the warranty has lapsed and it doesn't work anymore. Companies are apparently betting on that and it's an environmental travesty.

Yes, I know. I said this exact thing above.

The parent said these devices used "custom batteries", implying that Honeywell et al were custom-designing and manufacturing their own special nonstandard batteries just for these applications. This is incorrect, and needed to be corrected.

But it’s rare enough that it’s hard to find. So much so that it actually doesn’t make economical sense to find this (rare, at a premium) variant because it would cost about as much or more than a new light (which includes new batteries, ironically)

You can't pick up a standard 18650 battery at Walmart either, but that doesn't make it some kind of special battery. It's bog-standard. Availability at Walmart has nothing to do with something is standard or even common. Brake pads for some random mass-market 2015 model year car (GM, Toyota, etc.) are nothing special or difficult to find either, but you're not going to find them at Walmart.