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Comment by Willingham | Hacker News Reader

It is my understanding that small nuclear batteries output very little energy, so little in fact that they are virtually useless for most applications where a classical battery would be used. The upside is that they can produce power for decades without ever ‘charging’ or in this case, replacing the isotopes. In other words, the use cases aren’t as exciting as one would expect.

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They aren't a replacement for chemical batteries, more a complement. They're good for battery topping. Basically even when a device is completely off, its battery is still slowly losing power. This loss can be quite small, but if you leave a phone or something in a box for weeks, it'll be dead. This is not really an issue for consumer electronics, just charge it again. However there are applications where you want battery powered electronic devices that are ready to go when you need them and stored away from the electrical grid, like an emergency phone in a box on a remote hiking trail, or equipment in an emergency kit stored in a lifeboat, or a medical device in a first aid kit. By adding a nuclear battery, it can pump power in at roughly the same rate the battery would deplete itself when off, so even after years of sitting unused, your device still has a full battery the moment you turn it on.

Besides emergencies, there are also situations where the device has a low duty cycle, and thus its average power requirements are very low. For example a remote sensor that only activates for a few seconds per day may consume thousands of times more power for those few seconds than a nuclear battery could put out, but the rest of the time it could be recharging such that it has as much energy available the next time it turns on.

For most of the global, A solar cell can do the same thing. It's really only in the most northern and southern regions that a solar panel becomes ineffective.

What about sensors in a basement or pipe?

Depends on how accessible the pipe is. Consider that such a sensor needs to report data. If it's isolated enough then you need to run a transmission line anyways just to get at that data.

If we are talking about a basement with pipes, then power isn't likely too far away.

Sounds perfectly suited for watch batteries.

Until they reach the dump...

My wristwatch's "face" is a solar panel - Citizen Eco-Drive. Had it for around 20 years and it has never stopped.

I prefer changing the battery once every three years over having a radioactive emitter strapped to my wrist. There is a decent case for nuclear pacemakers since changing the battery of those requires surgery, and even there it didn't get traction. Watch batteries are quick to change, I don't see the risk/benefit tradeoff working.

And with smart watches we are back in "useless for most applications" territory.

Nah, too bulky and there are already better solutions. If you have just a classic watch, then a kinetic charging mechanism is something that's been around for ~100 years. Your watch auto-charges from simply wearing it and walking around.

But if you need more juice, then solar watches are also a thing that work pretty well.

For a smartwatch, these batteries won't produce enough power to keep them going. It's better to just slap a bigger battery into the watch rather than a nuclear battery + regular battery.

Watches tend to be exposed to light a fair bit, so putting a solar panel in the watchface easily outperforms a betavoltaic cell. This has been available for decades, and even some of the high-end Garmins have it.

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