These are my three standard issue 85AH Interstate batteries delivered by most RV dealers. You can notice the two caps on the top of the battery case. Just gently pull this cap up to see three holes in the top of the battery. If you can't lift up this plastic cap you may use a small flat blade screwdriver to pry with. Be cautious of the battery fluids as it will be very corrosive.
Just make sure the fluids are covering the tops of the internal cores. If one cell is low you can top it with DISTILLED water from local hardware store or auto parts store. WALMART carries distilled water in a gallon jug.
Again the battery fluid should just cover the tops the of the internal battery cell core. DO NOT OVERFILL
Hope this helps...