I maintain a small herd of iPhones for my family and friends. My daughter kept having very short battery life. I replaced it a second time thinking I had installed a bad replacement battery. I asked how she charged her phone. She would run it completely down until it threatened to shut down then, charge for a very minimum amount of time. She gave it just enough charge to get going again. Then out the door she went.
The mailman delivered her phone USPS Priority mail from South Carolina. I swapped the battery out, repacked it in the same Priority mail package, printed a new Priority Mail label and handed it back to him as he was delivering mail on the othe side of the street. Not bad I thought, about a ten minute turn around. So if we do the math that cost me $22 dollars in Priority Mail postage. I sent the spare to her with a prepaid return label, she sent me hers, I returned hers with a prepaid label to return the spare back to me.
I didn't want to give my daughter who is a grammar school teacher that has a masters degree a lecture on battery chemistry and the really boring facts from a high school graduate. I explained it in simple terms her fifth grade class would understand. If you get in your car to go on vacation think of your battery as a fuel storage tank. If you only put in a few gallons it will get you to the next town before you need more fuel. If you completely fill the fuel tank before you leave town then you will make it to your destination with fuel to spare. If you charge your iPhone just long enough to get the battery indicator to show 100% the tank is not actually full! You can still get a trickle from a partially filled tank, but it will soon run dry. The battery in the phone charges very quickly at first then slows down to prevent over heating but then keeps slowly filling the tank until it reaches full capacity then quits. Instead of trying to charge it for a few minutes in the morning before rushing out of the house. My recommendation is to always charge overnight. When you get ready for bed please put your iPhone to bed too, plug it in! The best battery charging practice is slow, low and long. My daughter replied "oh that's why it always seams to be dead”. My van has a thirty five gallon fuel that I never let get below a half tank. The younger generation wants just enough for now and does not have the patience to fill the tank and don’t want to put their cash in the gas tank either.