Battery Stamina

I got a laptop recently. The specs said that it has a battery life of upto 6 hours, ( the laptop is a Lenovo U41-70 80JV007GIN), but I want to know how much I can realistically expect. The battery is a 3-cell 45 watt-hour battery. The processor is an i5-5200U, the RAM is 4GB, and the graphics...