I've only used this jumper to start my lawn tractor. The first time, the battery was totally dead with the jumper connected. I used the boost option and the tractor started up. I noticed the voltage level on the jumper went from 100% to about 85% after using the boost option. I used the jumper several times during the day to restart the tractor, and after the voltage level dropped to 35%, I decided to connect the tractor to a battery charger. All in all, I am satisfied with this jumper and would recommend it to anyone.