I appreciate such softwares and possibilities, but I would not recommend using an old smartphone: continuously charging its battery represents a huge risk, history just reminds us about battery explosion, detective cables, defective wall chargers.
If you add also that batteries, when aging, are a real risk, then, thanks but no.
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.
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.
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.
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.
I'm currently integrating (project is on pause but one day!) an android tablet into an old car. And the battery was a dealbreaker.
So I've removed the battery and added an resistor to trick it into booting anyway. Only problem is that android think the battery is dead so it won't perform system updates unless I first charge it. Which I guess is fine in this case since the tablet is out of support anyway.
If you've ever wondered why cellphones don't work without a battery present at all, even when plugged in, it's because they're used as a capacitor effectively for the cellphone radio. The peak currents of those can exceed several amps momentarily so you need to have quite a lot of power on hand (even exceeding the charger) for times when you want to transmit. The amount of total energy being used from the cell is close to nothing however.
I'm surprised yours works at all, it must be fairly marginal.
All I can say is that it isn't an uncommon operation to do.
I have stress-tested it a bit and know that it won't be a problem for me, certainly not for the music and navigation I will be using it for. Also as far as radios go only wifi+bluetooth.
I wish phones would work with no battery when plugged in.
What resistor value, and where did you place the resistor to be able to boot without a battery?
Don't remember, if you are lucky there are guides for this for your particular device.
If I remember correctly there are four terminals, aside from power one of them might be battery temperature which I think is mandatory. I measured the resistance on the original and mimicked it. Basically hardcoding the temperature since I don't have a battery. But I could be very wrong on this. Google it first!
Looks like that could be mitigated by just flashing a new firmware. LineageOS (formerly CyanogenMod) has a long list of supported devices these days. Booting something more open source seems like a good idea for a long-running security camera app, as opposed to closed-source stock Android builds.
LineageOS is great, but I doubt it supports many $20 phones. Porting is done by volunteers - people who buy cheap phones are unlikely to make the effort.
Also, in theory a rootkit could go into the embedded firmware or use a closed source kernel module. In fairness, that's not a big threat yet - cheap devices tend to get cheap rootkits...
If you add also that batteries, when aging, are a real risk, then, thanks but no.