Answer

The screen resolution display setting will not have that much of an impact on run time.  The screen brightness, CPU clock rate, and HDD activity levels will have more of an affect, along with wireless network use.   Max run times are listed at 3.5 hours with the 8 cell. 

Features and benefits:

• 8 cell
• 14.8 V dc
• Lithium Ion (Li-Ion)
• Delivers up to 3.5 hours of system run time
• Over-discharge protection
• Offers proven battery technology with balanced performance, capacity, and longevity protection
• Backed by a one-year limited warranty with renowned Service and Support from Lenovo

Performance specifications:

• Color: Black
• Output voltage: 14.8 V
• Capacity: 5400 mAH
• Charge time (power off): 3.5 hours maximum

Note: Battery life (and recharge times) will vary based on many factors including screen brightness, applications, features, power management, battery conditioning, and other customer preferences.

Physical specifications:

• Approximate height: 19.8mm (0.78inch)
• Approximate width: 92.5mm (3.64inch)
• Approximate length: 259mm (10.20inch)
• Approximate weight: 535g (1.18lb)

Additional information available on Lenovo's support site.

http://www-307.ibm.com/pc/support/site.wss/MIGR-74240.html