The percentage displayed on the device is a percentage of usable charge, not total volts in the battery. The phone will shut down before voltage gets anywhere near low enough to damage the battery.

All that does wear them out is cycling them, so you can keep it happy for longer if you charge regularly and do not discharge below 50% often.

The most important metric to battery health is regular charge and discharge. Don't leave it discharged, or constantly plugged in to power. This is what often kills laptop batteries that are constantly on AC power.

There is no need to fully discharge any battery in any Apple device before charging it, and yes, that is a bad idea. This concept comes from nickel–cadmium batteries, which are stored discharged and generally work better when they are fully discharged prior to charging. Apple hasn't used a ni-cad in anything for a very, very, very long time.

 

Wow thanks for the information guys. Since I've gotten my Iphone I've always let it die completely before I recharge as I thought that was the best way to keep the longevity of the battery. This was the trick to home phones back in the day and I thought it applied to all phones.

So Simba when do you recommend I recharge? At 50% or let it drop to 20%? Should I ever let it go down to 0% and shut down as I've been doing?

Once again thanks for your help guys. Rep to you both.

 

There is no hard and fast rule, and you shouldn't worry about the phone getting too low or always having to recharge at a certain percentage. Best practice is just not to run it down all the way too often, and make sure it doesn't sit on the charger all the time either. The batteries are supposed to be "memoryless" but that doesn't mean running them to 0% repeatedly is good for them either. I usually keep my battery above 50%, and I've had no issues, I charge it in the car usually around mid day for a bit, and then up to 100% at home before removing it from the charger.

In summation, be aware of where the battery is, but no need to be neurotic about charging.

 

If you can, charge at 50% or above. You won't hurt anything charging at 20% or 0% or anything in between, but going below 50% will add another full cycle to the battery. That will have a very slight but culminative affect on battery life.

 

Yeah, the first week I got my 4S battery was terrible. Would have to charge it everyday (despite the FW update). Bought a mophie juicepack and then one day realized that bluetooth was switched on (facepalm) but funny enough it was not showing the bluetooth icon in the notification bar.

To improve battery performance
- Set autolock to 1 min
- reduce brightness a little
- switch of bluetooth and location services (unless you really need them)

Made a significant difference for me. With the juice pack I get 2 days guaranteed, 3 if I am lucky.

 

Going below 50% won't add a full cycle, as the battery counts cycles in a more finite way. Even if you charge and discharge the battery partially 5 times and the total adds up to a 100% discharge it still counts as a full cycle. The only way to avoid that would be to leave the phone plugged in all the time, but that's equally as detrimental. Obviously charging more often will slow the time it takes to complete a full charge cycle significantly, but I've never heard the 50% explanation before.

Here is the apple link explaining their batteries: Apple - Batteries

 

They cycle faster when regularly taken below 50%, even with similar use/charge patterns.

Regardless, battery health can be summarized thusly: Charge and use the device frequently. The most critical aspect to battery life is to keep electrons moving.