Is there a battery monitoring app that can send a notification when the battery reaches X %? I would especially love an app where you could customize the percentage at which point the app will send a notification (for example, 80%). I looked at some battery apps I found on AppStore, but none of them had this feature. The reason I'd like to have this feature is I want to unplug the charger before the battery hits 100%. Or at the very least, know when I have hit 100%. I don't want to have the phone plugged any more than necessary since that will cause damage to the battery.

I read that the optimal range (for the battery in the long run) would be somewhere around 70% and 80%, i.e. you would try to keep the battery percentage in that interval at all times. It would be easier to maintain this if my phone sent me a notification whenever I reached one of the two points, as I can't use all my time checking the battery.

Does such an app exist? 

EDIT: I don't have a MacBook. I'm looking for an app for iPhone.
There is an app called Coconut Battery that does this but it is hardwired for certain values all less than 50%.  There is also a setting for number of minutes left. Load the app and go to Preferences under the coconutBattery menu item. This opens a panel and one option is Notifications. See image below.



CoconutBattery is free but there is a Pro version for $9.99. This will also report on iOS devices connected to your computer.