Under the top step in the entry stairwell. You should see a small latch on the front of the step riser that holds down the tread. Once you unlatch it you lift the tread and maneuver it out of the way. There should be one 12v Flooded Lead Acid battery there - unless if your house batteries are in there too. Some have both house and chassis batteries under the step and some just have the chassis battery there. With the house batteries in another location..
You would find this info in your Operator's Manual in Section 6-7
Here's a link to a digital copy of your Operator's Manual in case you don't have a printed one:
https://www.winnebago.com/Admin/Publ...Suncruiser.pdf
Here's a screenshot of the chassis Battery details:
Linear Mode
