Odd battery Issue

Hello.
I have a 2.16ghz white macbook 2.5 years old.
recently my battery began to make problems causing the computer to shut at once at any given point ( evan at around 80%charge).
I ordered a new battery from ebay. Once installed it was hard to make the new battery calibrate with macbook. system profiler show 5549mAh.
The X sign showed up constantly. also the battey used to make same shut down problem at around 22 -25% charge.
after many restarts ( holding 5 seconds power button, p+r reset...) and calibration drills, I get the battery to work fine but now showing only 3800mAh. also have to mention that calibration didn't success fully because at 4% the computer shuted itself down without safe sleep.
also, when i have my palm pressing down the left part of the macbook ( left of the trackpad) the x sign is on again and the magsafe led turns green for few seconds..( all lights on battery itself are green and look fine)
did my battery burned out some parts of it? or was it 3800 at the begining but the computer didn't acknowledged it? Help!