I want to ensure that a mobile phone is always charged, without requiring manual intervention: e.g. disconnecting/reconnecting the charger, switching the charger on/off, et cetera). One idea would be to leave the phone always connected to its charger, which in turn would always be connected to the AC mains. How feasible / practical is this? And are there better approaches?
Note that I am unable to make changes to the phone, because it is an off-the-shelf, commercial phone. But I can make changes to the circuit of the charger.
Edit: This is not a specific phone model I am talking about, but potentially a phone I'd buy, for a very specific purpose. This might be lower-end Android smartphone. The phone would be left in an unattended remote property, and serve as a landline replacement (since the area isn't served by fixed-line phones). A caretaker would use it periodically to report well-being, and share some video / pictures of the place by sending MMS multimedia messages. The place has bad power supply, and thus the I want to keep the phone always charged. I do not want to hand over the phone to the caretaker, since he doesn't live on the property.