iPhone Battery Charging

July 8, 2007 7:04 PM

We've all been reading about the iPhone and its battery that's supposed to last 300-400 charges. How do they define "charge"? I usually charge mine every night, when the battery is at about 50%. Is that a "charge"? If I top my iPhone off when it's at 80%, is that a charge? What's the best way to preserve the life of my iPhone battery?
posted by yizzle to technology (10 comments total)

Apple Batteries
A charge cycle means using all of the battery’s power, but that doesn’t necessarily mean a single charge. For instance, you could listen to your iPod for a few hours one day, using half its power, and then recharge it fully. If you did the same thing the next day, it would count as one charge cycle, not two, so you may take several days to complete a cycle. Each time you complete a charge cycle, it diminishes battery capacity slightly, but you can put notebook, iPod, and iPhone batteries through many charge cycles before they will only hold 80% of original battery capacity.
posted by birdherder at 7:17 PM on July 8, 2007 [1 favorite]

The iPhone (and iPod and almost every laptop produced in the past five years) uses a lithium ion battery. There are a number of resources available on how to treat a lithium-ion battery.
posted by deadfather at 7:22 PM on July 8, 2007

What Apple said was that capacity will start to degrade after about 400 charges. That doesn't mean it stops working, just that a full charge lasts for a shorter amount of time, like most batteries. When new a laptop gives you x hours, after a couple of years you maybe get x/2 hours.

A full-charge life of 400 cycles before degradation sounded quite good to me, but I await an AskMe correction.
posted by bonaldi at 8:59 PM on July 8, 2007

The lithium battery will degrade over time anyway - even if you never use it at all, so it no matter what you do you'll still need to buy a new battery after a while, so consider that it's probably not worth adjusting your life to best fit the battery - just use the device as you want to, and expect to replace the battery in a year or two. Budget for it if you think that will help. I'm all for thrift, but you blew $500 on a luxury phone, so let it be your luxury.

Technology should work for you and work around your needs, not the other way around.
posted by -harlequin- at 9:34 PM on July 8, 2007

I once read a 30+ page paper online about lithium ion / lithium polymer batteries.
It was targeted more at laptop batteries, but should apply here as well.

The short, as i remember it:
The batteries like to stay charged (ie not drained all the way), so if it's convenient for you to plug it in, do so (but dont obsess).
Heat will shorten battery life, especially if the battery is fully charged when exposed to the heat.

Worst possible scenario is leaving the device charging in a hot car or direct sunlight.

Don't obsess. If anything, just start putting your change in a jar, and by the time you need a new battery you'll be able to replace it.
posted by itheearl at 10:03 PM on July 8, 2007

Seconding "don't obsess". It's not as doom-and-gloom as the technobloggers make it sound. After 300-400 charges of the entire capacity of the battery, the battery will hold less charge. It won't be completely unable to hold a charge. Let's look at it this way:

I've had mine for a week and used it a decent amount. I've had to apply the equivalent of a 100% charge just a little more than twice. (That is, I give it little charges here and there, and the total amount I've charged it has come to a bit over 200%.) Math break:

One "charge" means "charging the equivalent of 100% capacity of the battery" for this discussion.

If I apply a charge once per week, and I get 300 (low end) charges before significant degradation, I'll over five years before the battery starts kicking the bucket. But that's unrealistic, right? If you want to get a general idea of how long the battery is probably going to be "like new", here's the formula:

Let N = Number of expected charges
Let C = Charges per week, varies from person to person
Let W = Number of weeks in a year
Let R = Some random manufacturing variance
Let Y = Years until you'll see significant degradation in the performance of the battery

N / (C * W) * R = Y

Okay, so I charged a little more than twice in the last week. That means it'll be over a couple of years before I want to send it in for battery replacement. If we use the high number of 400 charges (R could give us this transformation), we get significantly better results, but we can't really be guaranteed to get that.
posted by Mikey-San at 3:19 AM on July 9, 2007 [1 favorite]

Ok....
I found that website i was talking about.

Just DONT spend all day reading it, there's way too much info there.

http://www.batteryuniversity.com/

And you probably want "how to prolong lithium-based batteries":

http://www.batteryuniversity.com/parttwo-34.htm
posted by itheearl at 6:29 PM on July 9, 2007

A full-charge life of 400 cycles before degradation sounded quite good to me, but I await an AskMe correction.

Well.. The battery has already started to degrade by the time you buy the phone. So, it isn't a question of '400 cycles before degredation' at all. They probably mean something like 80% capacity after 400 charge cycles, which is the same as any other battery.
Or.. It is about the same as NiMH, which I've used a lot. I don't know what the typical numbers are for lithium ion, and I have very little experience with them.
posted by Chuckles at 8:49 PM on July 9, 2007

The battery university page and the Apple page (and every other source I've found that claims to be authoritative about how li-ion batteries work in practice) have conflicting information.

See this previous AskMe thread about extending the life of laptop batteries, which has some details about the inconsistencies, and what I think is a reasonable conclusion - "Your battery will lose charge over time, resulting in somewhere between a 2 and 3 year lifespan [...] over that time, the maximum per-charge capacity will slowly decrease. If you manage to charge cycle the battery more than around 800 times in that time, the life will be even shorter."

There's also some discussion on that page about the apparent hand waving with regard to what constitutes a charge cycle and why I think the official Apple explanation is incorrect.
posted by Caviar at 8:16 AM on July 10, 2007

I'd still trust battery university - they seem like they know their stuff, and they arent trying to dumb it down.
posted by itheearl at 10:01 PM on July 10, 2007