This is different to what Apple say on their site about battery life.

For example they say that running the battery down to absolute zero at least once a month is good for its lifespan.

http://www.apple.com/batteries/iphone.html

I am also greatly instead in the question of iPhone / IPod Touch battery life, so would love clarification of these issues.

Esp concerned about the 500 charges thing. What I read, but I can't find it now, is something like that the battery life drops 20% after 500 charges. Not quite the same as "only good for 500 charges". If that's wrong, I want to know!

PS I see that the Forum thread you posted is based on what a guy remembers the Apple engineer saying at a talk "a month or two back". The possibility of having misremembered or misunderstood is high.

Btw Rob, got any refs about hearing issues "significant amount of background noise and you're trying to distinguish a particular sound"?

I have never been into listening to music very loud, but I do seem to find it harder than other people to listen to conversation in a place like a busy bar where there's a lot of background noise.

Btw, worth noting that Apple can replace the batteries.

$79 + $6.95 shipping. Not cheap, but less than buying a new iPhone/iTouch.

http://www.apple.com/batteries/replacements.html

Thanks Rob. Don't worry about the music - we're talking about earbuds here, and I have yet to actually wake up with them still in my ears :). While the iPod stays on, it does not continually blast music into my brain. The question was primarily about the battery life of the iPhone.

"I am also greatly instead in the question of iPhone / IPod Touch battery life, so would love clarification of these issues. Esp concerned about the 500 charges thing."

The battery life is a hot topic in Mac circles. Apple does not subscribe to an open source hardware design philosophy and this includes their (as you pointed out) expensive batteries. There is little documentation on the exact number of charge cycles that an iPhone has. In the past, as mentioned in that slashdot article, Apple seems to have squashed some of the studies that have been done.

Contact a 3rd party Apple Repair / modification shop in your area. Often, these are found around College campuses. For first-hand information, ask them how many charges they estimate an iPod is capable of. This ~500 number is the basis of my information and the URL I provided above backs it up. Since there isn't a lot of information about this limitation online, I suggest that if you're concerned, you talk to a 3rd party repair shop.

A solid understanding of battery and DC technology would help us uncover the real numbers behind your question. Since it's off-topic, I won't comment much, but I'll point out these links:

Apple's definition of a "Charge Cycle" is important:
http://www.apple.com/batteries/

One of the most referenced articles on Lithium Ion batteries:
http://www.buchmann.ca/Article5-Page1.asp

The complete (user contributed of course) Wikipedia article:
http://en.wikipedia.org/wiki/Lithium_ion_battery#cite_note-18

"Rob, got any refs about hearing issues "significant amount of background noise and you're trying to distinguish a particular sound"

As with many teachers, working closely with Audiologists is an important part of the gig. Hearing impairments are responsible for a large number of learning related misdiagnoses. I have a good amount of experience in this area. While I always defer to an Audiologist for a proper diagnosis (as should anyone), the causes and symptoms are pretty easy to understand.

Again, without delving too far into the subject, here are some links for more information:

http://www.ehealthmd.com/library/hearingloss/HL_causes.html

http://www.healthscout.com/ency/68/598/main.html

http://hcd2.bupa.co.uk/fact_sheets/Mosby_factsheets/Hearing_Loss.html

In short, any sustained irregular noise will damage or change your ability to hear. I believe that this fact is "by design" / "part of evolution". People who regularly spend time in noisy environments can hear perfectly fine in those environments but cannot if displaced.

Sustaining in-ear noise for many hours at a time regularly, every night, will change the way that your eardrum and ossicles interpret sound.

Thanks Rob, info on both batteries and hearing much appreciated!

Can hear fine in normal circumstances, but sometimes not in a bar or party.

Ok, I found a reference that reflects what I remembered. The official Apple position seems to be that the iPhone battery will lose 20% of its capacity after 400 full charge and discharge cycles. i.e. A full charge will then last you 80% of the time it did when brand new.

http://www.macworld.com/article/58916/2007/07/iphonebattery.html

Any reason to doubt that?

"unless you're completely draining your battery every day and charging it back up completely every night, you shouldn't have anything to worry about for the life of your iPhone"

http://www.tuaw.com/2007/07/12/macworld-clears-up-confusion-around-iphone-charge-cycles/