Probably dead Chassis batteries or very low. Either way/reason, the alternator probably was NOT charging them while the engine was running. I experienced a similar problem developing last time I had an appointment to have work done on my 97 Serengeti/Cat300. Started fine, but I noted the step was a bit slow retracting. Didn't think about it until I was halfway to the RV Fixit place. I always monitor the Intelli-Drive and noted that the alternator output was only around 12 vdc and sometimes 11 vdc. When I got to the RV Fixit Place, I told the tech about the reading. Instead of jumping right into what I was scheduled for, put a multimeter on it. He said he could giggle the "Sense Wire" and get a good 13 vdc reading but it would drop back to the lower setting. He diagnoise it as a bad/corroded sense wire connector. Cut the old one off and put a new one on and waaaaaaaaa la consistent good reading.
By the way, please drop by the two Safari Yahoo websites and Join The Zoos. Lots of good Safari Info and helpful folks to boot.