Originally Posted by ksnwireless
2 1/2 years for a Lithium-ion Battery is a long lifetime. Their normal life expectancy is about 1 year. There is no memory effect with Lithium-ion Batteries.
You'll have a surface charge with no load, which may indicate 1/2 scale. As soon as there is a load (transmitting or working the CPU), there's maybe enough drop, to shut-down your phone.
I believe you can purchase a new Battery for around $20 USD..
ksnwireless is right- There is no power loss on a litium ion battery. It will put out the rated voltage until there is none left. Unlike NiCads that lower the power down as it looses it's juice. NiMH are similar to Litium Ion as they are more prone to failure to due heat and cold.
As far as the life of your battery the litium ion can only take som many charged. They do not get a memory. So if they are not lasting daily run cycle of the specs of the phone you need to replace the battery. You got a full extra year than most batteries.