Does World Clock eat the battery?

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Level 2

242 points

Does World Clock eat the battery?

I had three cities in World Clock and listening to podcasts all day (9-6), I never got to the low battery warning (20%). I added a fourth city and suddenly the battery life dramatically decreased even though I listened less to the iPod part.

Is this coincidence or does the Clock app put demands on the battery even when it is not active? Is there something where a certain number of cities starts to demand much more than that number minus one?

I understand that third parties still don't have push notification even after it was promised, and I assume that is because Apple is pretty fanatical about preserving battery life and couldn't make push available to developers without diminishing battery life too much. Of course, the apps that come with the iPhone probably have special access to the system, that is, they can consume juice even when they are not active.

I would like to hear from anyone who has information or similar experience. Thanks.

Mac mini 2009, iBook, eMac, 2 iPhones, AppleTV, Mac OS X (10.5.6)

Posted on Apr 28, 2009 9:29 PM

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Answer 1

Best reply

Allan Sampson

Level 10

123,677 points

Apr 28, 2009 9:49 PM in response to David Trevas

I can't provide any documentation, but I don't believe adding more cities to the World Clock or having more than 3 reduces battery life significantly, so this was likely a coincidence.

I understand that third parties still don't have push notification even after it was promised, and I assume that is because Apple is pretty fanatical about preserving battery life and couldn't make push available to developers without diminishing battery life too much.

If you watch the sneak preview for firmware update 3.0 to be released this summer which will include push notification for 3rd party developers that want to make use of it for their app, Apple provides the reasons why they were delayed in making push notification available for 3rd party apps.

Of course, the apps that come with the iPhone probably have special access to the system, that is, they can consume juice even when they are not active.

Apps like the phone app, the iPod, Safari, the address book, Calendar, SMS, and the Mail client have special access to the system - are allowed to be used at the same time and run in the background.

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Answer 2

David Trevas Author

Level 2

242 points

May 2, 2009 8:21 AM in response to Allan Sampson

After I wrote that post on Tuesday night, I deleted three of the four world clocks. My battery life for Wed., Thurs. and Fri. was back to normal. I didn't change anything else.

I can't imagine why the World Clock feature of Clock would consume any power at all. All it does is add offsets to the current time. All of the other tabs (Alarm, Stopwatch and Timer), when engaged, need constant attention even when running in the background, but I can't see why World Clock would require any resources whatsoever. The math involved could be applied instantaneously anytime a redraw is needed.

I'd like to hear the experiences of people who have changed the number of world clocks they used and if they noticed any change in battery life. My experience is summarized here:

1 clock: Battery easily lasts through 9 hour day with no recharge.
3 clocks: Battery may get to 20% low battery warning after 9 hours.
4 clocks: Battery half-full after about 4 hours, 20% warning at about 6.

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