iPhone 4 battery questions
This is from everythingicafe.com which is an unofficial source, but I have heard this same information about batteries many times:


  So, what else can you do to increase your battery life? Charge it
  often. I’m serious! Apple uses Lithium Polymer batteries (not a
  straight lithium ion!), which perform best when you keep them “topped
  off”, meaning if you have a chance to charge it, then do it. I
  generally never let myself get below 45% unless testing due to what
  seems like unusual battery drainage. Apple also recommends that once a
  month you drain the battery down below 10% and then fully
  (uninterrupted) charge back to 100%. This is more for the battery
  meter than anything. It helps the meter get a correct reading on the
  battery and not display inaccurate information.
  
  Source


Charging at least once a month keeps the electrons moving occasionally.

You can read what Apple officially says about batteries and how to maximize battery life.