The long and short of the iPhone's battery

Gues s what? The more you use your iPhone, the faster its battery drains. This is hardly a surprise.

Further, certain iPhone features require a bit of extra power and will drain the phone's battery even faster. Again, not much of a surprise. It's simply a matter of physics.

Still, it's worth pointing out exactly what these battery-eating features are. It may be of particular interest to iPhone 3G owners, many of whom claim that the 3G's battery life is significantly shorter than that of the original iPhone.

In its iPhone User Guide, Apple offers several tips as to what to turn off in order to conserve battery life:

    On page 86, Apple states: "To conserve battery life, turn Locations Services off when you’re not using it."

    On page 102, Apple states: "You might want to turn Push conserve battery life."

    Later on the same page, Apple adds: "When Push is off or for accounts that do not support push, data can still be “fetched." For optimal battery life, don’t fetch too frequently."

    On page 104, Apple further notes: "Using 3G...may decrease battery life. If you’re making a lot of phone calls, you may want to turn 3G off to extend battery life."

On its "Batteries - iPhone" page, Apple offers additional battery-saving tips. These include: (a) Turn off Wi-Fi; (b) Turn off Bluetooth; (c) Use Airplane Mode in low- or no-coverage areas; and (d) Minimize use of third-party applications (especially games that prevent the screen from dimming or shutting off or applications that use location services).

Apple also suggests turning off the display for video podcasts, and just listening to the audio. It similarly follows that watching any extended video (such as a movie) should be avoided if you need to preserve your iPhone's battery for other higher priority tasks.

Of course, all of this can be taken to impractical extremes. I can imagine a satiric skit about the iPhone battery, with the punch line advising that the best way to maximize the life of your iPhone's battery is to turn off the iPhone altogether and never use it.

Battery life and the iPhone 3G

But seriously folks, what about the iPhone 3G? Does it really eat up a battery faster than an original iPhone? I've read several articles on this subject and have done some informal testing on my own. My (still a bit tentative) conclusion is that, when settings between an original iPhone and a 3G are the same, they use up the battery at about the same rate. The biggest reason that 3G users may see increased battery drain is due, not to the hardware, but to the new 2.0 software: Location services, push, downloaded games and the like. However, as these items are available to original iPhone owners as well, they shorten battery life on any iPhone (or iPod touch!). It is only the 3G service itself that may lead to a faster decline in battery life on an iPhone 3G. And while keeping 3G enabled does appear to take a toll, I have not found it to be a dramatic difference. In any case, the iPhone 3G is competitive with other 3G smartphones (as shown in this chart from PCWorld).

The 3G's mystery battery drain

There is one irritating exception to the above generalizations. There is a battery drain that occasionally happens with my 3G but never with my original iPhone or iPod touch. It is quite dramatic and, unfortunately, I still don't know the cause.

Perhaps once a week or so, the life drains out of my iPhone 3G's battery at an alarming rate, even when the iPhone is sleeping! For example, my iPhone may still have about 80% power left at the end of the day. As such, I may decide not to connect it to a charger. The next morning, I turn it on and find the red "low battery" warning on the screen, claiming I now have less than 10% battery power left. My original iPhone and iPod touch, on the other hand, show almost no battery decline during this same period. I have seen numerous similar reports but still have not found a solid explanation.

My current theory is that the iPhone is activated by some process while sleeping, such as the arrival of a text message or a phone call or a pushed email. For some reason (presumably due to a bug that affects the 3G but not original iPhones), the 3G doesn't correctly go back to sleep after this. Instead, it stays in some quasi-active state and begins to drain the battery as if I were actually using the phone. The next morning, when I finally wake it up, the battery charge is almost gone.

I have experimented to see if some particular iPhone feature (such as having push or 3G enabled) is the primary trigger for this symptom. Apparently not. I still have these occasional battery drains, whether these features are on or off. Hopefully, an iPhone firmware update will eventually resolve this problem. [Meanwhile, if you believe you know what is going on here, please email me to let me know!]

What else to do...

Assuming your use of the iPhone demands that most or all of its battery-draining features remain enabled -- and that your iPhone is losing its charge more quickly than you would like, what can you do?

• Charge your iPhone's battery every night. At least you'll always start the day with a full charge.

Apple also notes: "It’s go through at least one charge cycle per month (charging the battery to 100% and then completely running it down)." Otherwise, the length of time that a charge lasts will decrease.

• Keep an extra charger in your car and/or at your office -- so you can charge your iPhone "on the go." Just be aware that "the iPhone 3G cannot be charged with a FireWire power adapter or FireWire-based car charger."

• If you charge your iPhone by connecting it to your Mac, make sure your Mac does not go to sleep while charging. Apple warns: "If your iPhone is connected to a computer that’s turned off or is in sleep or standby mode, the iPhone battery may drain."

• Consider getting an external battery for your iPhone, such as the Kensington Battery Pack and Charger. Such devices can be especially useful when you won't have access to a power source for an extended time, such as when on an airplane. You can watch a movie on your phone and still have a separate full charge left for the remainder of the day.

Finally, you can hope that Apple one day releases an iPhone with a replaceable battery. That way, you could carry around a spare battery and swap it when needed. This is what I routinely do with my digital camera. It would be great to have the same capability for the iPhone. But I'm not holding my breath here. Apple hasn't yet offered a replaceable battery for any iPod or iPhone. I'm not expecting them to change their policy any time soon. But I can still hope.