Wonder if I should replace my battery in Late 2011 MBP

My Late 2011 MBP has decreased its battery charge from 4 hrs to 3hrs until zero. It has 500 cycles, about half of the drop dead Apple Battery Specs of 1,000 cycles for my battery.

Saw that OWC has new one for $100. Wonder if anyone replaced their battery in a similar MBP, how hard R&R and what results they got in added Battery Charge.