Titanium battery life

[musicarteca]

Hi all,

I have had a Titanium Powerbook 550 MHz for a couple of years now, and the battery is performing with a much shorter time than before (about an hour or less depending on the use). I have done the charge, completely discharge, charge thing, and still it doesn't last longer. The questions are: How do I know if there is time to buy a new battery? How many years should they last with regular use? Is there a software test that I can perform to see if I need a new battery or if I can extend the usage time of the present one?