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Comment by RL_Quine | Hacker News Reader

It’s really a non concern. Realistically if there was a problem it would present in normal usage when people are charging them in bed.

The amount of superstition about lithium batteries is crazy, given how many of them are used in any household on a daily basis. The battery is functionally not being used if a phone is plugged in and the battery isn’t drained. This misinformation comes back from when people were using Nickel Cadmium cells decades ago, those cells were functionally continuously charged because it caused absolutely no harm to them.

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The difference is that a phone might get hot when the camera is running 24/7 and CPU load is high, e.g. due to motion detection.

To add some anecdata: I had an old iPhone (IIRC a 4s) running as security cam for about 6 weeks. When I returned, the case was cracked due to a swollen battery.

....and? I imagine the phone shut down and literally nothing happened? Batteries are kind of designed to do that in case of cell failure, actual fires are incredibly rare.

Care to elaborate your software setup?

I have left old phones plugged in because I used them with wifi in the workshop. More than once I had to quit using a certain phone because the bulging battery started getting hot.

Granted they were 5+ years old but its there.

Two major differences:

The battery will be charged to 100% constantly.

The battery will be much older and has worse capacity than most consider even usable.

remove the battery and leave it plugged in

Would expect this to work only if by plugging in you mean plugging in 3.7V to where the battery's terminals were.

Can't recall succeeding to boot an Android phone with USB charger and no battery.

Nexus One works fine without a battery, but that's an absolutely ancient phone by any standard.

The battery also has a built-in charge controller to prevent overcharging, and if the capacity is significantly lower, shouldn't the risk of that stored energy being released also be lower since there's less energy stored?

The phone has an on board charger. The battery itself has its own controller which will disconnect the battery from the charger if it goes over voltage, under voltage, or over temperature.

The "percentage charge" of a lithium cell isn't really any measure of its safety. Even at 0% charge the cells can still auto ignite, there's an incredible amount of energy in them when they're considered to be empty.

The problem is lithium doesn't like being at 100% state of charge for prolonged periods of time. Normally you charge it up, then use the battery. When on a charger the voltage will sit close to fully charged voltage, and that ages the battery quickly. Add some heat and you may have a problem eventually.

In my experience, its usually "only" a problem when later, you discharge the battery and then try charging it back up, thats when stuff starts burning.

> The battery will be charged to 100% constantly.

So? That's a non-statement as far as safety goes. It's as relevant as the color of my shirt, or the current date, or the state of the moon.

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