Hi JITH IN,
When was the last time the battery charged for 100%? Are you using an original Dell adapter for this model? Is the adapter frayed? When the adapter is plugged in to the system, does the adapter stay firm or does it fall off easily? Does the system overheat? Does the battery get very hot? If so, remove the battery and let it cool down to room temperature for about 2 hours and then try connecting and charging the battery.
Update the BIOS - http://dell.to/1G6xT8d
Restart and press f2 key to enter BIOS - check the adapter status in BIOS and the battery health(if available).
Remove the battery and check the battery health meter by pressing the battery gauge.
If the battery is old and is not durable, then you could get the battery replaced.
Assuming there is no warranty, then you could contact our team to get a quote for a battery (if in stock) - http://dell.to/1vnT6CQ
You could also get the battery from a 3rd party Dell parts seller - http://bit.ly/1tq2f31
My personal suggestion, is that, if you are using the system in one place, then you could continue using the system with the adapter plugged in - as a desktop machine and that you could invest your money on a new machine.
Let us know if you have any other queries.