As a new owner of an 81 Westie with the original 2L aircooled engine, and a
new list reader, I thought I would check out and advise of my battery
situation in the hope that it helps.

My aux battery is an East Penn Mfg Part# 640RMF, 810 CA, 650 CCA, 105RC,
Group 40R installed in Oct 2014.  Bought from nationwide-battery.com. I
just had it tested at the local auto store and it has a
remaining battery life of 46 months according to the electronic test
machine.  Not bad for a 6 year old battery.  No idea of its previous life
of course.

The vehicle battery is a Motomaster (Canadian Tire) product# 10-9100-4,
Group 91, CCA 700@ 0 F / 850@ 32F, Reserve Capacity 100 Min installed in
Feb 2015.  I have not had it tested.  As previously noted by others, the
recommended battery is a Group 41 (for Canada).

Both batteries fit the their respective places nicely and seem to do the
job ok.  This summer will reveal more about their suitability.