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Comment by barbegal | Hacker News Reader

Not comparable to a real battery any time soon based on the paper https://pubs.rsc.org/en/content/articlelanding/2025/cc/d4cc0...

> The perovskite betavoltaic cell achieved impressive parameters, including a short-circuit current density of 15.01 nA cm−2, an open-circuit voltage of 2.75 mV, and an energy conversion efficiency of 1.83%, all of which represent significant improvements over previous works.

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Will it ever be comparable to a "real" battery? The energy output has a clear upper limit. Are there materials that produce only beta particles at a high enough rate per gram that could power a cell phone with a half life of more than a few days?

Assuming you could get these to 10% efficiency (which is theoretically possible) and a phone needs 0.2W of energy to function then you would need a source capable of supplying 2W of energy (of which 1.8W would be dissipated as heat). The phone would be fairly hot all the time but 2W could be dissipated without it overheating in most environments. Strontium 90 generates 0.95 W/g so in theory a few grams of strontium 90 would be enough to power your phone for many decades (the half life is 28 years). But if someone were to accidentally put such a phone into an insulating material it might overheat and become a dangerous radioactive mess!

> and a phone needs 0.2W of energy to function

For an arbitrary definition of "function". I don't think a modern phone would achieve a meaningful function at that level. The cellular modem alone blows past that budget many times over. Even an old rotary phone went over 1W.

Apple's efficient 5G "C1" modem used in the iPhone 16e is still at ~0.7W. The Qualcomm models used in the iPhone 16 are 0.8-0.9W.

It might charge a capacitor/"real battery" most of the day and then be available when needed.

At the end of the day if the phone draws more power than the power source provides, you're limited to bursts of activity until the capacitor is depleted and then the phone is dead while the capacitor recharges. 0.2W is barely enough to power an idling phone, let alone charge an extra capacitor.

Today we juggle with ~15+Wh batteries (the "capacitor") and 30+W fast chargers (the "power source") and still need better.

It doesn't need to replace conventional charging. But a phone that gained charge when unused might still be useful - being able to make a call later might be better than never.

It would be great if used as an "emergency power source". I see this equivalent to the satellite SOS systems - not useful for daily use but essential in emergencies. You know you can get brief emergency function every x hours.

But for the question asked higher in the thread, it would never be comparable to a "real" battery. This would be a very special purpose battery.

If you found such a material, would you want it in your pocket? Or someone else's pocket, where it could break in an accident?

You are right. They are definitely not ordinary consumer products. However, they might be useful where recharging or exchanging a battery is impossible or associated with serious disadvantages.

For example, in the past cardiac pacemakers had been used with nuclear batteries. However, there is a risk that the pacemaker will be “forgotten” after death, and something that is actually radioactive hazardous waste will be disposed of via crematoria or cemeteries.

Another area of application for nuclear batteries is space exploration.

I think the tradition is someone else's pocket in some other country.

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