My vaio battery charges only upto 80%. Why is that so? It also tends to discharge too fast providing less working time. How to proceed to obtain 100% charge?
This usually happens with older batteries when they are simply unable to hold a full charge.
Is it an old battery, say more than a couple of years old? If so, you might want to think about replacing it with a shiny new one.
Microsoft have a troubleshooting page for laptop batteries which mentions this.