I usually add that as far as the trucks hour meter, [in the 8 hours drive time in a battery cycle of 8-8-8] if you get 5 or 6 hours on the hour meter before you reach the battery meter's 20% remaining mark (which is when it it time to head to the charger) , that is about a good '8 hour shift' run.
The 8 hours cooling down time is every bit as important as the charge or run time too... don't allow a battery that is still hot/warm to the touch on the outside case to be put into service and don't allow 'quick charging' as the physics of a large lead acid battery do not respond well to less than proper charge cycles.