Using an Automation APP like Tasker to turn off a Home Assistant-controlled smart plug when the battery exceeds a reprogramming threshold, might be a more reliable method & works for any device.
This is the method I have been using for years and it works great. I use Home Assistant to manage the automation, the Home Assistant client app for Android (you could use tasker for this) to collect the device telemetry to send to Home Assistant (how it knows when the battery hits 85% or drops below 70%).
I do want to point out there is one small downside to this method: your device charger (and I'm using an Anker wireless phone charging stand as my charger) only works for one device. Example, say my personal phone is charged up to 85%, so I take it off the charger, but my work-issued phone needs to be charged, but when I put my work phone on the charger nothing happens and it doesn't charge because the charger is connected to a smart plug that's turned off because my personal phone is charged up.
I tried a similar scenario: The phone has a nfc reader built in, so I put the tag on the charger and tried letting the phone read it, but quickly discovered that android can't/wont read nfc tags unless the phone is unlocked, which defeated the elegance of the solution. I hadn't considered buying a standalone reader and attaching the tag to the phones, that sounds a lot more complicated.