Recently I got some bad advice from an Apple Genius at the Apple Store near the Plaza Hotel in Manhattan. He advised me that I should let my battery run down to 5% or lower as often as possible in order to maximize the battery life. This is not the way to get the most out of your iPhone's lithium battery.
Apple makes clear on its official site, that, "There’s no need to let it discharge 100% before recharging. Apple lithium-ion batteries work in charge cycles. You complete one charge cycle when you’ve used (discharged) an amount that equals 100% of your battery’s capacity — but not necessarily all from one charge." Xfinity, Comcast's, internet, cable and telephone service, explains on its mobile phone information site, that phones using nickel ion batteries had a memory charge problem that required a full charge to be depleted so each section of the battery could be continuously used. Phones with lithium batteries should not be fully discharged each day. "[I]f you let your battery drain completely every day, it will last 500 days. If you charge it before it drains and top it off throughout the day, you’ll stretch out the time those 500 charges will last."
A Popular Science article recommends letting the battery life go down to only about 50% per cent before recharging and avoiding recharging fully. "Shallow discharges and recharges are better than full ones, because they put less stress on the battery, so it lasts longer."
Battery University provides detailed research into this issue. "If at all possible, avoid full discharges and charge the battery more often between uses." The lower the discharge percentage, the higher the number of discharge cycles.