iPhone OS 3.0 was released back in June and with it came many of the features iPhone owners had been clamoring for, such as MMS capability, cut/copy/paste and so on. Now that those qualms are behind us, it is safe to say that the most common complaint among iPhone and iPod touch owners is sub-par battery life.

In an effort to keep the iPhone's design smooth and uniform, Apple has chosen to forgo a removable battery. Love it or hate it, iPhone owners are forced to pay attention to battery life more so than owners of other handsets, since keeping a second charged battery on hand is not an option.

Most iPhone owners are willing to sacrifice a removable battery in order to keep their handset of choice of course, but that's not to say all is lost where battery life is concerned. There are several measures that can be taken to drastically improve the battery performance -- some at little or no cost to usability or convenience.

1. Charge responsibly

Most people tend to get into the habit of charging phones overnight. While there is certainly much debate regarding whether or not charging habits affect battery life and longevity, many experts agree that over-charging a Lithium Ion battery can definitely reduce its performance over time. In other words, over time a full charge will not last as long for someone who regularly leaves his or her iPhone plugged in overnight as it would for someone who unplugs the iPhone once it is fully charged.

As a general rule, try to wait until your phone battery is nearly empty before charging it. Once your battery is full, unplug it from its charger. Getting into this habit is good for your battery and it is good for the environment as well. The batteries in the iPod touch, iPhone, iPhone 3G and iPhone 3GS charge in about an hour or less, so there is certainly no reason to leave your handset plugged in overnight while you sleep.

2. Get a second charger

This may seem like common sense to some, but buying a second charger for your office is a great way to help ensure that your iPhone never runs out of juice. Some people carry one charger between their home and job but it's just too easy to forget it while rushing. A second iPhone charger can be purchased on eBay for as little as $7 shipped. Car chargers are just as inexpensive, so those who spend a fair amount of time on the road would be well served to consider one as well.

3. Get a portable charger

Frequent flyers and those who spend a good deal of time on the go with infrequent access to a wall outlet should certainly consider purchasing a portable charger. The most common form of portable charger consists of a battery pack, a cable and a variety of connector tips to ensure compatibility with a wide variety of devices. While just about every option these days includes an iPhone/iPod touch adapter tip, two recommendations are the USB TurboCharger 3400 by Proporta (3400 mAh) and the Solar Charger by Devotec Industries (1800 mAh).

4. Adjust display brightness

A very simple tweak that will have a dramatic impact on iPhone and iPod touch battery life is decreasing the display brightness. Apple uses fantastic displays in its portable devices but they require a significant amount of power to illuminate them. The good news however, is that they are still extremely viewable when the brightness is turned down. Try lowering the brightness in Settings -> Brightness to between 60% - 75%, the lower the better of course.

5. Adjust auto-lock

Further to number 4 above, the less time your display is on, the better. In Settings -> General -> Auto-Lock, choose the 1 Minute option.

6. Turn off Bluetooth when not in use

Bluetooth headsets and car kits are fantastically convenient but when they're not in use, Bluetooth should be turned off. Bluetooth on the iPhone is constantly searching for a new device to connect with when it is not in use and unfortunately, there is no way to turn the search feature off. While powering a Bluetooth radio takes a minimal amount of energy, the constant searching will indeed dramatically reduce battery life.

7. Adjust data fetch settings

A smartphone's ability to keep email, contacts and calendar items in sync over the air is an absolute necessity. The process of connecting to remote servers and exchanging data however, is an obvious drain on the battery. The iPhone is no exception of course, but Apple has given users a great deal of control over how often the iPhone fetches new data. In Settings -> Mail, Contacts, Calendars -> Fetch New Data, try setting Fetch to Every 30 Minutes or even Hourly if possible.

Moreover, for email or calendar accounts that are used infrequently go to Settings -> Mail, Contacts, Calendars -> Fetch New Data -> Advanced. Set each trivial account to Manual rather than Fetch. With this setting configured, these accounts will only retrieve new data when their relative applications are opened. So, email accounts set to Manual will only grab new emails when the Mail app is opened and calendar accounts will only sync when the Calendar app is opened.

8. The Wi-Fi debacle

Wi-Fi is another big area of debate in terms of iPhone battery life. Logic might dictate that if Wi-Fi is on, energy is being used so the result will be shorter battery life. In practice however, moving data via Wi-Fi requires much less power than moving data via 3G. As such, many find that leaving Wi-Fi on will actually increase battery life -- dramatically in fact. If you don't often have access to a Wi-Fi network then obviously this tip is not for you. For those who have wireless networks at home, at the office or at a local coffee shop however, the more you can use Wi-Fi, the better.

9. Keep GPS usage to a minimum

Unlike Wi-Fi, there is really no question that GPS usage is hard on the iPhone battery. While the temptation to play with a new voice-guided navigation app can be overwhelming at times, try to avoid using it as a novelty to navigate known areas. Similarly, Location Based Service (LBS) apps like Yelp, Layar and others will deplete the iPhone battery at a rapid rate, so use them sparingly.

10. Turn off vibration

In public areas and other noisy environments, a phone's vibrate function is absolutely essential. In quieter environments where you will definitely hear your iPhone's audio notifications however, disable the vibrate feature by going to Settings -> Sounds and toggling Vibrate under the Ring heading to off. Similarly, disable the vibrate feature within games and other apps whenever possible.

11. Disable iPod EQ

Ensuring Settings -> iPod -> EQ is set to off will have a major impact on battery life, especially for heavy iPod users. Some of the EQ settings in Apple's iPod app will make your music sound amazing but the cost to battery life is far too significant to leave EQ enabled all the time.

12. Don't update apps while on the go

There's nothing better than finding out one of your favorite apps finally received an update, but try to wait until you're connected to Wi-Fi before downloading any updates. Each time an app is updated, the full application file must be downloaded from the App Store. If the app is large, downloading it over 3G will undoubtedly impact battery life negatively. Downloads over Wi-Fi are much faster and require significantly less power. The best option however, is to wait until you're connected to your computer and to download any app updates in iTunes on your Mac or PC. To apply the newly downloaded updates, simply sync your iPhone.

13. Don't download music/videos while on the go

Just as app updates can often be large files that will result in significant battery consumption, music and video files purchased from iTunes are even larger. Sometimes downloading on the go is necessary but if you can, wait for a Wi-Fi connection to minimize the impact on your battery. If possible of course, make music and video purchases on your computer and sync the new files across to your iPhone or iPod touch.

14. Always apply OS updates

Any time Apple issues an update to the iPhone OS, apply the update. New features aside, Apple often makes tweaks that have a positive impact on battery life and the only way to obtain them is by updating your OS.

15. Disable 3G on the iPhone 3G and iPhone 3GS

This tip should only be used if absolutely necessary of course, but 3G is without question a battery killer. If you absolutely need to stretch your battery life out for as long as possible, disabling 3G is the best way to do just that. Go to Settings -> General -> Network and toggle 3G to off. Note that data speeds will be reduced and the phone will no longer support simultaneous voice and data while 3G is disabled.

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