I had an Optima D27 in mine for a while, but was then told by my panel beater that it had dropped a cell whilst in their workshop and needed to be replaced. It turned out it was actually the alternator, but I had no choice but to buy a new replacement battery at the time.
I thought about getting another AGM, but they are very expensive up here off the shelf and the auto elecs reckon that they just don't last up here in the heat and with the vibrations from unsealed roads etc.
So I just decided to go into the local Repco and grab one of these for around $220 on sale:
https://www.repco.com.au/en/search/?text=DIN85
They are manufactured by Century Yuasa and come with a 30mth warranty, so that's good enough for me. Cranks the CRD no probs and has been great for the 6mths I have had it.