Easy battle penalty

The Easy battle penalty is a experience penalty for fighting monsters that are too low level for your current combat level. It starts when you get to be 6 levels above what you are fighting, and becomes 1% higher for each level beyond 6. For example, if you are level 44 fighting something level 18, you have a 26 level difference and get a 20% experience penalty.

It is unknown if there is a cap to the penalty.