I seem to be repeating this stuff quite often, so about time I put it up here and just point people to it.
Last year my iBook's battery started deteriorating and eventually died. It barely lasted 2 years. So I did a bit of searching around and found a lot of interesting information which is essential knowledge for anyone using Lithium Ion(Li+) batteries, which today is anyone with a laptop, mobile phone, camera, media-player(iPods and the like) with built-in rechargeable batteries.
Over the past few years most equipment manufacturers have been replacing NiCd/NiMH batteries with Li+ batteries because they offer better energy density(lighter than NiCD/NiMH for the same capacity of charge), but most people are unaware that they need to be treated differently.
Here are some facts about Li+ batteries...
What it basically means is that if your mobile phone is fully drained by the end of the day. The battery will die by the end of the year and will need to be replaced. Even if your phone lasts for days at a stretch the battery will still be dead in 2-3 years from the date of manufacture of the battery and not the date you started using it.
Same goes for laptops, if you are constantly running your notebook on battery expect it to die well before the 2-3 year limit.
I think I pretty much wore out both my iBook's and S55's batteries in the approx. 2 months that I spent at my parents place in 2005 when I was using the iBook and GPRS extensively and would unplug them when they were fully charged. And was doing 2-3 cycles per day on average.
Now that I'm done with the scary part, here are some tips to extend battery life.
Charge Frequently, anytime you can charge the device or run it off the mains, you are saving your battery.
Avoid Full Recharges, a full recharge cycle results in the battery getting heated which reduces it's life. So avoid them as much as possible. However battery charge indicators on laptops need calibration from time to time which requires a full discharge/recharge cycle. This needs to be done around once a month to keep the readings accurate.
Avoid High Temperatures, high temperatures are bad for your battery if you have a laptop with poor ventilation, consider running it off the mains with the battery removed when compiling stuff or doing other CPU intensive operations that heat up the machine. In case of mobile phones/cameras/mp3 players avoid leaving them in places with high temperatures like parked cars.
While buying new devices...
If you aren't the kind of person that replaces all their electronic gadgets every couple of years avoid buying devices without user-replaceable batteries A mp3 player or digital camera that runs off regular AA/AAA batteries will last you much longer than the 2-3 years that one with a built-in Lithium Ion battery will.
Most manufacturers don't expect you to be using the device past the life the of the battery. Or even worse they expect you to buy a new one when the battery dies by ensuring the battery isn't user-replaceable.
As most Lithium Ion batteries come in proprietary/non-standard shapes/sizes there is no guarantee that you'll be able to find a replacement battery when your current battery dies. Or the equipment manufacturer will fleece you with ridiculously high rates since they'll be the only ones who can supply you with those batteries.
If you are interested in learning more about batteries of all kinds, Battery University is an excellent resource.