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Comment by tjoff | Hacker News Reader

If only batteries were still easily removable...

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.

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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!

You can get a $20 Android phone with a camera and removable battery nowadays.

Camera, removable battery and X% chance of having a preinstalled rootkit (e.g. [0]). It's better to pay a bit more in order to have peace of mind.

[0] https://arstechnica.com/information-technology/2016/11/power...

Not a problem if you plan to wipe and root the phone yourself.

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...

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