Dell Inspiron 1545 dying when unplugged

[Salil]

I have a Dell Inspiron 1545 and about a year ago I started getting messages saying my battery was dying. I bought a new extended battery online(not from Dell) and replaced the old one. However, the new battery behaves exactly as the old one. It charges up from 0 to 100 in less than a minute and as soon as the laptop is unplugged the laptop dies as if there is no battery plugged in. How do I check the battery or is there some setting that makes the laptop think that the battery has no power?