With our 280 amp Sprinter auxiliary alternator kit, you will have a whopping 150 charging amps at idle! These would be dedicated amps used to recharge coach batteries fast! Your stock alternator will only have an extra 25-35 amps available for charging after it takes care of the 120 amps or so needed to run your Sprinter. The kit includes an external regulator that will give you 3 stage charging for proper charging and conditioning of your coach battery bank. The kit is available for the 2007 and newer 3.0L Sprinter and the 2.1L 4 cylinders. It can not be installed if your Sprinter has an auxiliary A/C system. Depending on alternator load and driving conditions, your fuel economy may suffer .5 or so mpg.