Not a 'green oval' vehicle, but had a OE Motaquip battery on a relatives Talbot Horizon that lasted 10 years. Was garaged and only covered 50,000 in that time.
The OE LR ones seem to last very well. They used Delphi, Lucas/Yuasa and Varta - in fact I have a L322 (110Ah) Varta one in my freelander now and thats 5 years old.
Guess it depends on the load it has to turn over and the frequency of use.
Dad still on original in 5yr old disco 2 (80,000 miles)
Regards,
Steve