Re: What do you want your cellphone to do?
I think a similar idea already exists. I can switch my phone to power saving mode which underclocks the phone’s processor, switches the phone to a grayscale display and limits the number of app I can use. I don’t know if there is an option that sends the phone to power saving mode once the battery levels drops to a specific level. Even if such a feature is not available out of the box, I’m sure there is an app for that or you could just put together a custom ROM for your phone that does this.