1st check there is no problem with the charger take out the battery and try using the laptop only with the charger if your laptop working fine then there must be problem with the battery.
Before replacing try this:
Remove the battery, and AC power. If you have access to the battery contacts inside of the battery compartment (in some laptops it's very accessible, others its almost impossible) try cleaning the connection terminals with rubbing alcohol and a Q-tip. It may not be getting the proper connection necessary to charge, recharge, and report battery information to the laptop.
Even after trying above step your battery is not charging then replace it with new one.
Noways there are different types of replacement battery are available in the market you can try one one of them.
http://www.123discoun.../laptop-batteries.asp
Note: While purchasing any laptop parts, you should always check the compatibility, model, part no. etc using the manual/manufacturer's website or take professional advice if needed.
Hope this will help.