Most phones won't boot without the battery. Obvious workaround is to connect a power supply (and large cap) directly to the BMS, but in my experience most phones will shut themselves down when they think they've drawn more than the capacity of their battery, even if the voltage is still high. You can sometimes get around that by rebooting the device every couple of hours (and there might be a software/firmware fix in some cases?), but it's a lot less annoying to just accept a small risk of a house fire.
You could throw the phone in an ammo canister, if the wifi AP is close enough. When I was building hobby quadcopters, which requires several ~half-pound batteries that are a chemistry optimized for maximum power density, a lot of guys recommended steel ammo cans for battery storage.
Afaik mobile electronics’ power circuitry is designed so that power goes straight from charging port to the processor, without constantly charging/discharging the battery, once charging is complete. Unless the system suddenly draws a lot of power (more than the charger is supplying) - which is unlikely in a smartphone.
Some phones bypass the battery when plugged in, but not all do. I know it's advertised as a feature of some gaming phones because graphics-intensive gaming is one use case where you'd want to use the phone heavily while plugged in.
Some newer phones support bypass charging, which powers the phone directly instead of continuously cycling the battery. Mine doesn't support that, unfortunately, so I've limited charging to 80% to reduce battery stress.
would've been better
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> built in battery backup
Isn't it always recommended to remove battery if you plan to use a phone or a laptop as a server? ( Fire hazard )
or is it fine to just limit the charging to 80%?
But in other hand, it is probably a pain in the ass to remove the battery and do some workarounds to make sure the phone correctly behaves without it.