2003 Toyota 4Runner Open Alternator Diode?

This past weekend the battery in my truck went dead over night. I had driven it home at about 1am with no problems, and when I went to start it in the morning, all I got was clicks. As far as I know, it had not had any symptoms of low battery leading up to this event, and I didn't leave my lights on (although I did have an adapter in my cigerrette lighter that aplits it into two outlets - one of which was used and one unused - I udnno if that had any effect).
I successfully jumped it using my friends cables and his truck and drove to where I needed to go (aproxmately 4-5 miles away). Upon returning to my vehicle I attempted to start it again on its own and only got clicks again. I contacted my roadside assistance company who came out to jump me again, but informed me that it should have been charged enough in the time I drove to be able to start itself again, and that my battery was probably shot. I live in the Arizona Sonoron desert, so I figured he could be right, and agreed to buy a new battery that he had in his van right there on the spot. He installed the battery and was able to start it up no problems, and then informed me he was going to run some sort of diagnostic on my vehicle. He hooked a device up to my battery terminals and reved the engine several times, and then printed out some computer results, informing me that my alternator has an opn diode. He said that was probably reponsible for why my first battery was drained and would most likely kill this new batterey within 48 hours if I don't have the problem fixed. He also advised me to remove the cables on my battery terminals whenever I parked. The new battery comes with a 6 year warranty but he made me sign that I would have the problem corrected within 48 hours or else my warranty would be voided.
Unfortunately, all of this occured late on a saturday afternoon, and I was leaving town monday morning so there was no way for me to get the problem addressed. I also don't own any tools and am unable to remove the cables with my leatherman, so I just left them on. I drove around normally the rest of saturday, sunday and monday morning. I got back from my trip yesterday (thursday) and when I got to my car in the parking lot at the airport, it started up without a hiccup.

Do I really need to get this "problem" addressed? Is this a reliable way of testing alternator diodes?