I was checking out the control systems on my Yukon in the driveway yesterday with my Tech II, and about 20-30 minutes into it, my Tech II started going crazy, and eventually ended up with a white screen. Suspecting a low voltage issue, I decided to start the truck, and it did not turn over. I connected my second battery with the quick disconnects, and it started right up. And, the Tech II started running properly again.
So, after 20-30 minutes with the ignition in the On position, my primary battery was dead. I put the battery on my pulse charger, and I'll be purchasing a new battery in the near future.
In retrospect, this was an unanticipated, but a good verification test, for having a second battery available in the truck. I was in my driveway, but I could have been anywhere, and stranded, without the availability of the second battery. I'm glad that I made that second battery with the quick disconnects setup on my truck.