For everyone reporting issues with their iPhone shutting down prematurely, with the battery Charge showing 30, 40, 50% etc. I did a lot of work in the Air Force on devices that used Batteries for their main power source. My Wife's iPhone started shutting down and she would complain to me that this started to happen more and more as time went on. Well after turning on the Battery Usage (batter percentage "On") I started monitoring when she would see the phone shut down. 4 weeks ago it was at 50% and she would hook up the cable to charge it. Then it would come back on and she would let it charge back to 100%. What she and others are failing to realize is that you are now creating what is called Battery Memory Lock. What has happened is the Battery is now setting a new power threshold. Meaning when the battery is showing 50% the Memory on the battery is telling the phone I am at 0% and the iPhone shuts down. I am still working to clear the battery memory lock on her phone and I have to do this one step at a time. The batteries current memory lock was at 85 percent, using my laptop I plugged in her iPhone cable into my USB port and am using the power cord that runs my laptop and charges its battery to charge her iPhone. But what I am not doing is charging the battery back to 100% First step - If you have Anti-Lock set to lock if you can for now set it to never you can than leave the phone main screen on to force the battery to drain. Note: If it is a corporate phone and you can't set it to never then set it to the max time for auto-lock, on my phone it is 5 minutes. Second step - as soon as the phone shuts down and you see the Plug - Charge symbol plug your cable into your laptop or desktop only until you see the iPhone initiate the powering up stage. As soon as you see the iPhone apple come on and you let the iPhone turn on (see the icon screen) immediately unplug the cable from your iPhone. Don't let the phone start to charge the battery. This should clear the current Memory lock on the iPhone Batter and I am currently waiting to see when the iPhone will attempt to shut off again (hitting another battery memory lock) So far her phone has been on for 2 hours since I did this and her battery life is now at 60% which is now 25% below where it was initially shutting down. This may not fix everyone's battery issue as batteries do go bad, but in most cases your iPhone has gotten a memory Lock because instead of letting the battery drain down to 0% people will charge their phones each time they go to bed or are done using the phone for day. Periodically allowing the iPhone to fully drain the battery to 0% will keep your iPhone battery or any phone battery from getting this Memory Lock. I hope this helps as it has helped me over the years in recognizing Battery Memory Lock and how to drain the battery past the Memory mark on the battery.