6TLs rather than group 31s on a military truck? Because 6TLs are standard military tactical vehicle batteries. Every wheeled and tracked tactical vehicle is set up to use the standardized battery. For example, imagine if the Army, with tens of thousands of tactical vehicles and hundreds of different configurations all had different sized batteries. A key aspect of US military sustainment is standardization whenever possible, why manufacture, warehouse, transport, train and maintain a hundred different kinds of automotive batteries when you can use one type. The advantage of simplicity far outweighs any disadvantages of using 6TL batteries as the standard. However, the quality of current AGM 6TLs leaves something to be desired. You're not the only one to report deficiencies with current manufacture AGM 6TLs.