BOAC, recent experience (yesterday) re-reminds me that a duff bios battery will also let it forget the date. This on a four month old machine - it was forgetting date and boot order.
So if your machine is not forgetting the date, it's not the battery.
Duff IDE cables have been a problem, but I've not had a SATA cable do that. Having said that, the plugs aren't that spiffing - got a loose one?