Robbbyr is correct - there are four coach batteries in the forward-most basement bay on the passenger side. The two chassis batteries are under the driver's seat and can be accessed through a removable panel just inside the driver's side door along the bottom. There are three or four screws that have to be removed to access the batteries.
The space isn't very big, so swapping out those batteries doesn't look like fun...
Ty & Deb Montag
2015 Jayco Seneca 36FK
2014 Honda CR-V toad