Thank you very much. Now the battery is charged up to 100% What I did was removing the battery and the connector for a while to release static electricity, and cleaning the connector and the jack. Now I can use this Vostro further. Mother board change is no option for me for this more than 10 years old PC
Battery of my Vostro 1550 can not be loaded recently even with the power cable connected. I've tried with a new battery, but still this problem is there. Battery loading status is going down dayly little by little. I guess, it might have something to do with BIOS or configuration. Does any of you have any idea ? 
Vostro 1550, Battery cannot be loaded