Thought I'd resurrect this tread as I've just decided to purchase one of the NVRAM chips.
Found these on ebay (
http://www.ebay.com.au/itm/190946708318?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649)
Bit of a cheaper option given that the lockwhenlit version cost $39 and another $25 for shipping to Aus. The ones of ebay cost $42 posted
.
As my TSPP does see a lot of use (more due to work commitments and kids), changing the batteries is likely to slip my mind so thought this would be the cheaper option in the long run.