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A number of complaints regarding the iPhone 3GS’ battery have surfaced on Apple‘s discussion board since the handset’s June 19 launch. Given Apple‘s promises of a faster and longer lasting iPhone, it’s understandable that 3GS users, particularly those who have made the jump from the previous models, have higher expectations.

Preliminary battery testing on our iPhone 3GS review model showed positive results. Until that time, I can offer tips on making your iPhone battery last. They can be used individually or in combination to best suit your own needs. Some of these ideas are even recommended by Apple and some of them we’ve mentioned on iPhone Atlas before.

Reset iPhone

In addition to resolving signal strength problems, resetting an iPhone can fix a faulty battery indicator and end applications that are improperly consuming the battery. Hold down the home and sleep buttons simultaneously until you see the white Apple logo indicating that your iPhone has restarted.

Restore with original settings

You can restore your iPhone by launching iTunes and selecting the Restore option on your iPhone‘s Summary page. This process will erase your iPhone‘s software and data, including all settings. You can restore them later via iTunes.

Drain the battery completely

Instead of charging it midway through a battery drain, add more juice only after the battery dies completely. A full drain may reset circuitry that prevents a full charge from occurring, despite indication of a full charge.

Force quit applications

If an application quits unexpectedly and you begin to notice poor battery life, relaunch the application, then force quit it by following the directions in this post. This can eliminate problematic or hung processes that might be draining the battery.

Lock your iPhone

Make sure that your iPhone goes to sleep automatically when not in use. You always can press the Sleep/Wake button, but even better is the Auto-Lock feature in the General section of the Settings menu.

Auto lock screen (Credit: David Martin)

Applications

Apps that keep the display from dimming or shutting off and that prevent your iPhone from sleeping can reduce battery life. This is particularly true for apps that use location services and push notifications. You can turn off Location Services in Settings > General menu. You’ll have to deactivate Push Notifications for each app individually, also in the Setting menu.

App Push Notification settings (Credit: David Martin)

Location Services toggle (Credit: David Martin)

Push notifications for email

The iPhone 3G’s Push functionality for Exchange and Mobile Me accounts also can destroy battery life. Turn this option off in Settings > Mail, Contacts, Calendars > Fetch New Data before restarting your iPhone. Messages sent to your push email accounts will now appear on your phone based on the global Fetch setting (every 15 minutes, every 30 minutes, hourly, or manually) rather than as they arrive. The manual Fetch setting will preserve the most battery life.

Push and Fetch (Credit: David Martin)

Checking fewer email accounts

Deleting email accounts or turning them off can preserve battery life as well. You can remove an email account in Settings > Mail, Contacts, Calendars, tap to choose an email account, and tap Delete Account. To turn an account off but leave it on the phone, go to Settings > Mail, Contacts, Calendars, tap to choose an email account, and set Account to Off.

Toggle email account on/off (Credit: David Martin)

Delete email account (Credit: David Martin)

Airplane mode

Even it you’re not flying, use the airplane mode while listening to music, watching a video, working in your favorite productivity app, or whenever you don’t want to be disturbed. Also, since constantly seeking a cellular connection also drains the iPhone‘s battery, the airplane mode is useful if you’re in an area with poor cellular coverage.

Airplane mode (Credit: David Martin)

Reset network settings

Restarting your iphone will delete any stored Wi-Fi passwords, DNS settings, and more. And in some cases it also can resolve signal strength issues. Find it in Settings > General > Reset > Reset Network Settings.

Reset network settings (Credit: David Martin)

Turn off Wi-Fi and/or Bluetooth

Be sure to turn off these features when not in use. Go to Settings > Wi-Fi and set Wi-Fi to Off. Go to Settings > General > Bluetooth and set Bluetooth to Off.

Toggle Bluetooth (Credit: David Martin)

Turn off 3G

The iPhone‘s 3G radio consumes a lot of juice so turning if off will save power. Go to Settings > General > Network and toggle Enable 3G to Off. You’ll be able to make and receive calls and access some data while 3G is off, though your iPhone will run on the slower EDGE or GPRS 2G network.

Enable/Disable 3G (Credit: David Martin)

Adjust brightness

Dimming the screen definitely can extend battery life. Go to Settings > Brightness and drag the slider left to lower brightness or right to increase brightness until you reach your desired settings. Turning off the Auto-Brightness settings also will help.

Brightness settings (Credit: David Martin)

Turn off the equalizer

Just like on the iPod, this feature can reduce battery life. Go to Settings > iPod > EQ and select Off. Yet, since EQ settings in iTunes migrate to the iPhone, you’ll have to override those settings and set the iPhone to Flat. Go to Settings > iPod > EQ and select Flat.

iPod EQ settings (Credit: David Martin)

iPod EQ options (Credit: David Martin)

More help

If you’re worried about your iPhone 3GS being defective, according to HardMac there is Apple‘s Procedure for Users Experiencing Short Battery Life with the iPhone 3GS. Also, if you’re still experiencing severe battery problems after trying some of these tips, it might be time to take a trip to your local Apple Genius Bar.

Personal experience

So far, my personal experience has been that my iPhone 3GS lasts a bit longer than the iPhone 3G, particularly after I tuned the iPhone 3GS’ features to meet my personal needs. Yet, it still doesn’t last more than a day with heavy use, unlike other smartphones.

One typically intense day started at 100 percent battery capacity at 5.00am. The battery then dipped to 80 percent at 9.30am, 64 percent at 12.30pm, 39 percent at 3.30pm, and 25 percent at 6.30pm before showing the 20 percent battery warning at 8.30pm. With my iPhone 3G, I used to get that warning prior to 6.30pm. And after tweaking my iPhone 3GS using the tips below, the battery showed 49 percent capacity after 15 hours of heavy use. That’s not bad for smartphone battery performance.

Are you experiencing problems with your iPhone battery? Got some tips to share that might help conserve battery life? What kind of activities do you do on your iPhone that deplete the battery faster? Let us know in the comments.

[This story was first published on CNET's iPhone Atlas blog.]