What is betterment, and why am I responsible?
In some cases the insurance company may charge you betterment on wear items such as batteries, tires, exhaust, etc. These items are routinely replaced based upon their life expectancy under normal use.
For example: You purchased a set of 4 new 60,000 mile tires last year; one of your tires was damaged in the accident and now you have to pay a 25% betterment. You’ve driven 15,000 miles since having them replaced, thus 25% of the tire has been worn off. The insurance company is willing to pay to replace the remaining 75% of the tire life expectancy on your new 60,000 mile tire.