The advice of a reputable dealer or a reputable battery service would be a starting guide.
The batteries will have a specification which the manufacturer engineered the vehicles operation to provide the most reliable service.
A mate of mine got almost 8 years from the two OE batteries in his LC 200 wagon.
I replaced the two original batteries with one but somewhat larger. I then used the space freed up on the driver side to fit a Provent catch can. I now also carry a jumpstarter but have never needed it.
