Do some reading about how to maximize the life of Lithium Ion batteries. Running on the battery if there is an opportunity to use the phone while plugged into a power source is just plain idiotic. Letting it run down is absolutely the worst possible thing to do. When sitting at a desk or somewhere near a power source having it always plugged in, will automatically turn off the charging once it reaches 100% and you can use it for long periods of time running just on the charging cable and giving the battery a rest. That's why you should leave it on the wireless charger or plugged into a charger overnight when sleeping as well - so all night long, the phone's battery is not forced to do work for no reason at all. The only time when the above is not really true is if you plan on replacing your phone every year. Then it doesn't really matter, as long as you don't repeatedly let the phone completely run out of juice.
Treating my phone the way I have as mentioned above, I've had phones 3 years old with batteries that perform as though they are brand new. That last statement is proof this is clearly the best way to treat a lithium ion battery.