The OEM battery is a VARTA 668 AGM. I bought mine a few weeks ago for R5,070.00 at Batteries4All in Centurion. They were one of the few suppliers that had stock. You could go with any AGM battery with a CCA of 800a. If you on a budget an EFB battery will work however, the CCA's wont match the AGM type batteries.
Alternatively try Evolution Wheel and Tyre in City Deep, Johannesburg. You can buy online but then you don't have the option to trade in your old battery.