The batteries on a 19 s2 chassis are located in the battery compartment with the house batteries. There are 6 located there 4 are house and 2 chassis.
As was stated, start by using the button on the dash. That will close the battery isolation module and utilize the house batteries as a boost. I have never used is so not sure but I believe you have to press and hold the button while you crank the engine. This also can be used to start the generator if your house batteries die.
If you want to go old school there are battery jump studs on passenger side rail below the engine. At least on the m2 chassis there are.
Linear Mode
