For the last week my 2000 F350 with 270000 miles has been feeling like it's cranking a little weak. Always starts but feels week. Anyways, yesterday I was attempting to get ANOTHER diesel engine started on a different vehicle by jumping is from my PSD. I hooked it to the other vehicle (an F800 boom truck with a Cummins) and the F800 still would not start. I checked my batteries on the F350 to make sure they were putting out good juice to my jumper cables: 14.3 volts. I left the PSD running the whole time btw. I also checked the F800 batteries and they had 12.2 and 12.3 volts, respectively. I walked inside the shop to get a tool for about 2 minutes and I came out and now MY TRUCK WAS NO LONGER RUNNING EITHER AND WAS DEAD AS COULD BE!!! Wouldnt even click when I tried to restart it. Hooked a tractor up to my truck and it fired right up as well as the F800 also. My question is, is there something wrong with my alternator or batteries (2 year old biggest Interstate batteries I could find)? Also, how do I test which one? I have jumped countless things before and never had anything like this happen before. O yea and since this my truck has started on it's own but still has that weak cranking feel. Thanks for any input!!!