You can either change it (not always that hard even with minimal soldering skills, it’s actually harder to find a decent battery), or use it plugged in. My wife’s old Kindle Fire is my permanently plugged-in, wall-mounted kitchen recipe book.

Someone in a different post mentioned the risk of fire/battery bulging if you leave your device plugged in like that. Is that a legitimate risk? I assumed that (while not great for battery life) there's some circuitry that's making sure it's not charging a whole lot.

modern devices often keep the battery at 80% level if charged for a long time, for this reason. (they say "to extend battery life" in notifications, and that might also be a side effect, but AFAIK the primary reason is to reduce the probability of bulging.

But many/most of these older devices discuss, do not - and my personal anecdote is that of the tens of phones+laptops I have owned myself and managed for family through the years - there were 4 cases of bulging: 3 were constantly-charging devices (as in, 3-5 years with hardly any time not charging), and one that was dropped from height and bulged immediately.

Hmm, since this is Android, would a rooted phone running AccA† to limit maximum charge work?

† https://github.com/MatteCarra/AccA/

Never heard or seen anything like that at all. The fact that you are not even given an option despite decades of "this really is one of the most important things to billions of devices" makes me a bit hesitant to believe it.

Maybe use a dummy battery? I use one for my 4g wifi modem. The battery got swollen so I replaced it with a dummy that connect directly to a USB charger.

Never thought of that, I’d assume/hope it has protective circuits… It’s been on there for close to 2 years with no issues.

You can use a plug with timer or even a smart plug that device itself turns on and off when battery level reaches certain levels.

Chargie [1] allows this for USB-A. It could be controlled via an Android app.

My problem with repurposing an old Android device is the security issues. Firmware doesn't get updated anymore. An alternative OS like LineageOS or PostmarketOS takes care of most of the software issues, but not the firmware itself.

Another issue is that the battery is going to be years old, and on 'recent old' Android devices its much more difficult to remove the battery.

[1] https://chargie.org

Not sure how great constant charging and recharging would be either ;)

agreed, though Qi wireless charging will increasingly make it easier