There are plenty of stories floating around these days, such as Apple faces mounting complaints on iPhone battery from MacWorld. I have an iPhone and have owned (and still do) a number of iPods and thus expect to be dealing with the battery issue any day now, except that I've never had a problem with even the oldest of my iPods. However, no matter what the various consumer groups say, I'm completely against an easily replaceable battery in the iPhone.
Frankly, I'm rather amused at the complaints coming out of the various sources about the iPhone battery not being user-replaceable. I have had a series of expensive phones and inexpensive ones over the years. When I first started buying them, talk time was such that even at an hour or two a day, I couldn't reasonably get by without a spare battery. Further, the chargers (complete with heavy wall-wart) were so unwieldy that I couldn't see carrying one of those back and forth. In lieu of buying separate chargers for each make (and, in some cases, model) of phone I was going to have, I decided that spare batteries were the right way to go. Unfortunately, that didn't work so well unless I was going to get up at 2am to change out the battery in the charger, or buy an optional charging base with the ability to charge two batteries at the same time. Mostly, I ended up purchasing car chargers (for each make and model of phone) and charging my phone whenever I jumped in the car in order to keep it charged up. These were lighter and less encumbering than the wall- wart-laden desk chargers and so I was reasonably happy with it.
Since the time that I moved away from actively using batteries to extend call time, I haven't used a spare battery. Note: I didn't say that I haven't purchased a spare battery, because I have for most of the phones for which they were available right up until about 2 years ago. Despite the fact that I change phones like a realtor changes cars, I still seemed to think that the batteries in those days died too quickly. This may have been true for the NiMH (Nickel Metal Hydride) and NiCAD (Nickel CADmium) batteries, but since we started using Lithium Ion batteries, talk time has become less of an issue and so have recharges.
As a general rule, I wouldn't buy a spare battery if I had the chance. Especially for the iPhone, with which I can use the small, clean iPod adaptor that I already was keeping in my briefcase to recharge the phone from my laptop anyway.
However, there's still the issue that some of the consumer groups are griping about claiming that the battery not being replaceable is just "wrong" and doesn't serve the public's interest. As a member of that public (I wonder how many of these lawyers and consumer groups are actually iPhone owners), I don't want the design restrictions that come with having a user-replaceable battery. There are tangible differences to the fit-and-finish that are necessary when you make a user replaceable batter to the phone. I don't want a case that pops open when I drop the phone (like has happened on almost every smart phone I've ever owned). I don't want a case that is an eighth of and inch or a quarter of an inch thicker to deal with the possibility that I'd need to replace the battery in 12-24 months. I don't want the poor reception that comes from putting the antenna someplace "safe" and away from the prying fingers of people who open up the phone. I don't want all of that extra plastic and insulating material that needs to be there in the cavity that contains the user-replaceable battery. And, I don't want the hook, or clip, or whatever is necessary to open the compartment.
In short, as a technologically-savvy iPhone user, I don't want a user replaceable battery.
The other issue that is coming up is the replacement cost of the battery. Apple is charging about $86 to replace it, plus another $30 for a 3 day rental of another iPhone. Now, I'm not sure if I could stand to be without my iPhone for 3 days, so perhaps, I'd rent, but I do have other GSM phones, which I could use with my existing iPhone SIM if I really needed to.
However, on the pricing issue, my P990i's battery retails for $69.99 and you can get knock-offs for $49.99. So, you're definitely paying a premium of between $17 (86-70) and $66 (30+86-50) to get the Apple product. Definitely a bit of a haircut, but in the grand scheme of things, it's a cost that I'm willing to deal with every 2-3 years for the function and form of the iPhone.
One man's opinion.