Thanks Kamold, it may well be the battery as you say.

I've done a bit of online searching for Varta batteries - specifically Batteries Direct:
- Silver Dynamic 572 402 075 - 750CCA - $265
- Silver Dynamic 585 400 080 - 800CCA - $316
- Silver Dynamic AGM 595 901 085 - 850CCA - $516

Is the OEM Yuasa battery an AGM? Is the extra cost offset by a longer life?