DVR stops recording on Highway

Hello, I am running into trouble on a series of ford 2015 E-450 paratransit vehicles, my company is the mobile video contractor and we have Installed a DVR with 6 cameras, 2 mics, GPS, wireless access point (the DVR powers all those accessories). Every day while these vehicles are on route (7 of them), the DVR will stop recording and it always seems to stop while the vehicle is going at least 45 mph. What is strange is that there are identical vehicles that were ordered later in the year that are working fine, and the wiring is the same among all of these vehicles. We swapped DVRs between a vehicle having the problem and one not having the problem, and the problem persisted on the same vehicle, so it seems to me that the problem has something to do with the power into the DVR. We have tried running our power directly to the battery (instead of the board in the overhead) and that did not fix the problem. The DVR will sometimes stop recording after about 40 minutes, and occasionally will run for 6 hours and never have a problem, but the problem does happen on most days. I am planning on installing a power conditioner later today, although I have never used one. I do not know much about alternators and voltage regulators but it seems to me that this issue could be related to that? Thanks in advance for any help I can get.

You say your running power straight to the battery so the Dvrs are 12 volt? Or are they 110 and your using Oman inverter. If your using the inverter I'd look at the inverters.Gary Sather