Looking for help
 

I am the engineer for our local Advanced Life Support unit and we are having what appear to be a strange electrical problems with 4 of our Expeditions. We have 1 2018, 1 2020 and 2 2021's all are having the same shut down problems. For no apparent reason they all will not start after running all day just fine. I have put jump boxes in all of them that works very well. The local dealers can not find nothing in the on board computer except a low battery voltage code which we know about. They were all outfitted by different companies so I don't think it has anything to do with the equipment. This happens about every 3 to 4 months with no warning or regulatory.
Anyone else having this problem or something like it? I find it very hard to believe that we have the only ones.
Thanks in advance