Note that limiting the maximum battery charge to something like 70 % would be more effective in those cases, completely avoiding the high voltages of a full charge.
However, even that seems absurd in such a use case. Does it matter if the old battery in an old phone gets worse? Especially when only used stationary anyway? Especially when the difference is sometime tiny like 5 % vs. 8 % (=3 % saved) capacity loss per year?
Say you leave it fully charged and you lose 10% usable capacity a year. 5 years in and you have a large-scale power outage, and you were smart enough to buy a beefy ups (and maintain that battery) to power your NAS and network equipment, but because you didn't with the phone, you lose DNS after like 2.5 hours (phone pihole) because the phone is dead. Now what are you going to do, just not look at porn on plex and weep because you can't browse lemmy in the dark? smh, forward thinking would have saved you. Now you gotta get the magazines to fap and make shitposts in mspaint until the grid comes back up.
Treat your batteries well. Enjoy your porn. Make power outages bearable.
Edit: I have a total of 4 ups units for a reason taps forehead
Does it matter if the old battery in an old phone gets worse?
I was under the impression long-term connection to power would lead to higher likelihood of battery swelling? But I don't know shit about batteries so I could easily be wrong.
I would prefer if I could power a device without needing a battery installed, but that design is rare these days.
If I’m using an old phone for a PiHole, the the battery is there to perform a safe shutdown when the power gets cut, basically a UPS to flush the write logs.
I don’t think it’s so much the charge circuitry as keeping the battery at 100% all of the time. keeping it plugged, but software limited to 80% capacity is probably better than letting it discharge.
Should be better better than just cooking it at 100%, but still not ideal in the long run. Ideally you'd bypass the battery entirely.
It's recommended to keep batteries at around 40-60% for storage while not in use. Not sure if keeping it around there would help when it's in use, but that could be worth looking into if bypassing isn't an option.