My example went something like this;
72 mo battery failed at 18 mos.
Retail price of battery was ~$150, let's call it $144 for simplicity sake.
$144 divided by 72 mos. is $2/mo.
The battery was in use for 18 mos. so a $36 dollar adjustment was offered against a $144 battery that can be bought outright for ~$100.
Didn't make much sense to me.