Or any PPC, laptop, or any other device with a Lithium Ion battery:
Charge your device as often as possible. If you have a power cord near you and you're staying in one place for a while, use it. Contrary to popular belief (probably ancient theory from back in the Nickel Cadmium days), frequent small charges are much better for a lithium-ion battery than running a full discharge/charge cycle on it. Discharging a Li-Ion battery fully and recharging it puts a lot of strain on the battery and will shorten its life. Another enemy to Li-Ion is heat. If your battery gets extremely hot, stop what you're doing, and let it cool down. Heat is the worst thing for a Lithium Ion battery, and will severely hurt its life.
Here are some resources (mostly for laptops, but they're about Lithium Ion batteries in general):
http://www.rm.com/Support/TechnicalA...?cref=TEC71629
http://news.tigerdirect.com/2008/02/...-your-battery/
http://answers.yahoo.com/question/in...4152547AAWBAXW
Hope this helps clear this issue up for some. I know this is a sometimes debated topic.