static can certainly be an issue
i would definitely check and see if the truck has a static strap on it and that it is contacting the floor.

One other possibility is if the operator is plugging the battery charger into the truck instead of the battery accidentally.
Although most chargers and trucks these days have a failsafe built into their systems to help prevent the charger from starting unless a battery is plugged into it i have seen this happen where the truck may hold a residual charge enough to cause the charger to start when plugged into the truck and that initial burst from the charger when it does start wipe out a controller or logic card or display unit.

in my experience the latter does not happen on that wide of a scale though so the static strap scenario would be my first guess.
As for the battery backup theory i usually find battery backup cells in the display unit... generally. Never have found one inside a controller, but then usually i'm not taking a controller apart when one fails.... generally ;o)