Battery life is the iPhone 3G's Achilles' heel. The original iPhone's battery life was marginal -- able to get through a full day of moderate usage, but only barely. The iPhone 3G's battery is worse, because of the energy-sucking needs of the 3G chipset.Poor battery life is one of the two three chief reasons why some people won't buy an iPhone. (The two other reasons: Lack of a hard keyboard, and overall phobia about buying Apple products, usually accompanied by self-righteous statements about how Apple fanboys are all sheep.)

Unlike other smartphones, the iPhone doesn't have a user-replaceable battery so you can keep a fully charged spare or two in your briefcase. Apple left off the user-replaceable battery because it adds bulk and weight, but, still, that leaves the iPhone straining to get through the day.

Apple has some tips for extending battery life on its Web site. Apple describes the tips as "commonsense pointers." I'd say they're actually blindingly obvious to anyone with any technical knowledge. But of course, many of Apple's users are technologically unsophisticated, so they can use more help. And a couple of the tips are useful even to power users.

Most of tips boil down to turning off features you're not using. Turn off 3G, location services, push e-mail, Wi-Fi, and Bluetooth if you're not using them. Adjust brightness. Minimize use of third-party applications like games that prevent the screen from dimming or shutting off, and applications that use location services.

Fetch new data, such as e-mail, less frequently. I found that made a huge difference on my first-generation iPhone. When I was out of the office all day, I set mail-polling to every hour, instead of the most frequent possible interval, every 15 minutes. Likewise, if you have more than one e-mail account, don't auto-check all of them.

Turn off the equalizer for song playlists.

Lock your phone when you're not using it, to be sure that nothing happens when you touch the screen. You just need to press the sleep/wake button at the top of the phone. And you can also set auto-lock to a short interval, such as a minute.

The tip I found the most interesting and potentially useful: "For proper maintenance of a lithium-based battery, it's important to keep the electrons in it moving occasionally. Be sure to go through at least one charge cycle per month (charging the battery to 100% and then completely running it down)."

There's an awful lot of rumors out there about whether to run your battery all the way down -- it used to be common wisdom that you should charge your battery fully every time, and run it down all the way every time you use it. Good to get the straight dope from Apple.

I'm going to be looking into battery extenders for the iPhone, and, alas, I feel they're going to be essential to anyone who wants to go more than about 12 hours between iPhone charges. I may even head back to the Apple Store today to check out the merchandise, assuming I can bear to return so soon.