iPhone 3g iOS4 Battery life

If you are using WiFi - turn it off unless needed. Apparently WiFi never hibernates while in standby. My 3Gs would heat up like a hand warmer even though it was off, and I was losing approximately 5% every 15 minutes. Once I turned it off, even with 3g in standby the battery lasted even longer than before teh ios4 upgrade. Sure hope there is a fix for this - at least a simple icon you can use to turn WiFi on and off instead of hunting through the Settings menu.

I'm Shocked, i had been using iOs4 since the beta 3 Became available, I used the GM until tonight and my battery life was simply reduced to a tiny fraction, while on standby my 3gs lost the half of it's charge in 8 hours, with wifi off and nno precesses in the background, never with any other pre-release firmware this happened

I have the same battery life issues with iPhone 3G after upgrading to iOS4. Very disappointing.

It seemed that I had lost battery charge, and that 90 minutes of charging had not raised the charge above the "red zone" (20%?)

Then I rebooted the 3G and after rebooting, the display told me I had 100% charge.

I would suggest a reboot. You might like to panic first like I did 😉

In case anybody from Apple is actually following this thread, I'd like to add my name to the list of unhappy users who have just seen their battery life plummet since last night after upgrading to iOS 4. As most users here have reported, my phone is not lasting through half the day sitting in my pocket, unused. Phone is not even 2 years old and I have never had issues with battery life before.

I had this exact issue and resolution too. My phone started getting warm and I thought it had shorted. After reboot, all is well.

Well I have to say I thought I was loosing my mind. Now I can have peace again. iOS4 on my 3g is terrible . I have to admit I did not expect much, considering this new os was not really intended to be installed on the 3g models, or were they... If I were a gambling man I would wager that, the man brilliant minds involved with the development of iOS4 new the entire time what kind of performance this update would really do to the 3g models. Steve Jobs did make a very very very brief statement to that effect in the keynote address. Could it be that apple just truly wants us all to upgrade to the 4G... hmm
i think i smell a conspiracy.. as for my 3g. my batter was drained after about 5hrs after a full charge.
not a single battery life issue until the update last night. Also the animations of the screens are slow and choppy and freeze up. I am going to reset my phone back to os 3.02 I can wait for my 4g ..

I have the same problem with my 3g. After upgrading to iOS4, my battery does not last a day in standby.

I think I know whats going on: Under iOS4, the 3g does not enter standby mode. If you look under settings/information, the time displayed for in use and standby is identical.

Is it possible to downgrade to 3.1.3 ?

My phone went from 100% to 93% over 8 hrs non-use; even though Wi-Fi was turned on...

We noticed this on one of our 3G iPhones, but a reset (as was suggested above) and a full charge sorted it out. Now battery use seems to be improved on our iPhone 3G overall.

Same battery problems here for two 3GS models. Very bad! After all this hype!

After a reboot and full loading, the problem is solved. This reminds me of a certain other operating system...

Since updating to iOS 4 on Monday night, battery life on my 3G has been awful. Fully charged at 08:30 this morning, completely dead by lunchtime. Hadn't even used the phone - no calls, emails, browsing - nothing.

Prior to Monday, it would last the full day early morning to late evening with quite intensive use. I have just plugged it in to charge again, and I will try rebooting and disabling WiFi, 3G, etc.