I successfully started a completely dead Kenworth T680 semi-truck using this brand new jump starter. Afterward, I recharged it, although I probably didn't need to at that time. A few days later, I used it to start another T680 that was also completely dead. This time, I didn't recharge it, and about a week later, it started a completely dead reefer unit. The reefer unit was so dead that I had to use the override feature. It started quite easily, but I immediately disconnected it, causing it to shut off. In hindsight, I should have kept it running for a few more seconds before disconnecting. This incident caused some inconvenience because the reefer unit takes a while to go through its startup cycle, and there's only a 60-second window to use the Yesper. This led to a few instances where I powered up the Yesper but couldn't use it, requiring me to restart the whole procedure. However, once I got the timing right, it started the reefer unit easily, and I made sure to let it run for several seconds before disconnecting the Yesper