my 64 beetle convertible (body by karmann, last of the wolf's heads, first year with a gas gauge), the 69 beetle and the 75 superbeetle convertible all had the battery under the right rear seat. only issue i ever had with the battery was when the '64 right rear floor panel rotted out and dropped the battery on a dirt road, piled up a bunch of leaves around the terminals as i dragged it down the road and started a fire. an interesting day.
beetle survived about 4 more years until 85 camaro ran through it with me in it. shoved the engine and tranny forward about a foot. i broke a wooden roof spar with my head. i'd still have it other than that minor issue. to this day the wife is still pissed about it even though it wasn't my fault.