Nikon D40 battery not holding charge? How to fix it? What's wrong?

I have had my Nikon D40 fro a couple of years now and have never had this problem.
I charge the battery for multiple hours until the bliking light stops then put it in my camera and its says it only has one bar left, but i know it has to be charged full from the time it had been charging.
What's wrong?
Do I have to spend MORE money on this camera and get a new battery?

These batteries don't last for ever… It's probably lived its life. Replace it.

The person who sold you your camera obused the Li-ion battery by leaving it uncharged for many days at a time.

If you keep your batteries fully charged, they should last for at least nine years (how long my Nikon D100 Li-ion batteries have lasted so far).

You may have to breakdown and buy another Nikon EN-EL9 battery

B&H Photo sells a Pearstone version for less than $20. The Nikon EN-EL9 battery costs about $60 direct from Nikon or at a Nikon dealer