mac Book air shows abttery loaded 99 % but still needs to plug the chager
This is typical when a lithium battery fails. You could buy a new battery or take it in for service in the unlikely instance that the charging circuitry is what has broken. Batteries are designed to fail and are consumable. The circuitry is far less likely to fail, but you can't tell the difference without servicing the hardware.

You can learn more at http://www.apple.com/batteries/ and perhaps see what your full charge cycle and other batter information show - that would perhaps reinforce the notion that it's time to get a battery replacement.



The System Information app can show your your power measurements.