Average battery lifespan of R51

[kirtan_a]

After a year and a half of usage, my R51 battery has become really bad. When I bought the Thinkpad, it used to give me between 3 to 4 hours of battery time. Now it is hardly 20 minutes. What is the average life span of the R51 battery?

My battery characteristics say
- Sony Li-Ion battery
- First Used Date - 2005-10
- Cycle count 263
- Battery health shows Red

I'm using Battery Maximiser Utility. What should I do/should have done to increase battery life? I mainly use the computer on AC power. Should I charge it to less than 100% (by adjusting the charging thresholds ?)