I'll drain now and then to calibrate. iPhone won't let a battery get dangerously low. It warns the user, then shuts itself off. The user has no way to drain the battery further into dangerous territory when it's in the phone and run down.
It made a huge difference for me. Since I got my iPhone I have been running it down to the 20-30% range in one day's use. Since I ran the battery down and recharged, after a full day's use I am ending up with around 70%. I've been charging every other day now. Much better.
I'm in the process of draining, but I'm so tired and I'm still at 16%. That's a first world problem for you. I would just let it go over night, but I have to work in the morning, sooooo.
Maybe the first time? I did it with mine. Came with 62% battery and I just felt safer draining it to 1% then charging it completely. I'm sure in the future you won't have to drain it before charging, but I usually make sure my iPhone is 95%-100% (at that point it seems like a trickle charging for the remaining 5%) before unplugging it. I do know that what you do with your battery and the cycles it goes through really have an impact on it. On my iPhone 4 I would plug it in to the charger every time I got in the car, giving it about a 5%-15% charge depending on how far I was going. That's just an example, I charged it similar ways in other situations. I later learned and realized that was probably a huge reason for it's really, really bad battery life it had. When I got my replacement I stopped charging it like that and it got tremendous battery life, a bit less than my 5 now; same backup and all!
I'm getting my iPhone replaced tomorrow (screen isn't flush and making popping sound) and based off what others have said it's not necessary for me to drain it completely when I first turn it on? If so that's awesome because it's really inconvenient to hold off plugging it in to to my computer to sync or restore from backup.
Draining my new i5 to 0% three times in a row DRAMATICALLY improved the battery life.
However, now that I've cycled it 3 times I will only be doing so like once a month.
Nobody is sure whether the new phone cycles help the software calibrate to give you more accurate readings or if it actually helps the battery itself. Probably the former.
This is exactly whats worked for me over the last 2 years.
I have the iPhone 5 now also and have done the above also. 24 hours STD BY with about 8 hours use no problems - wifi, lte etc all on.
My 4S, when I started to let it die completely and then charge it overnight, I would get way better battery than what people usually quoted.. again around 24-36 hours (but in Airplane mode overnight).
The battery seemed to be heaps better after about 3-4 weeks past from new.
I am 100% behind letting the battery die, then full charge overnight - even when its inconvenient to do so I do this and I have never had anything but battery success.
Damage the battery? No, sorry, never. This is false information, show me a test on an iPhone where this has occurred.