G'day Raff and Norm,
Here are the different sizes
https://www.centurybatteries.com.au/products/lawn-gardenhttps://www.ebay.com.au/sch/i.html?...;_nkw=ride+on+mower+battery&_sacat=0185x125x175 or 195x130x183
Most of my ride on mowers I would fit a small car battery ,new they were $60. saves spending $100. for a ride on battery,
but if you want the mower original fit a battery that fits the hole and if you are missing the clamps ,go to Bunnings and
get some 6 mm all thread and bent a couple of hooks and with some right angle steel make a battery clamp.
Cheers
Max.