I purchased lenovo z 570 laptop.clarification of regarding battery i am making 0 battery for every 15 days. (A) BATTERY is fully charged (100% ) , even though iam keeping plug in socket & using power for 4 hours continously.does it makes decreases battery life. (b) using up to battery power up to 10% & charge up to 100% .& repeat the same .does it makes increases battery life. which is better way to increase life of the battery

Not really, the older NiCad batteries get a memory effect if you keep charging from a half charged state, but modern Lithium batteries do not suffer from this problem.
If thelaptop battery is more than 3 - 4 years old then the battery could be worn out.These rechargeable batteries have a finite number of charge and discharge cycles andwill lose their charge capacity over time, i.e. won't charge to 100% andgradually the charge reduces until the battery won't charge up at all. OR Thebattery shows a 100% charge but when the adapter is disconnected the batterydrops off to zero capacity in a very short time. If the battery drops to anunacceptable charge level then the battery needs to be replaced.