>Years back, there was a TV ad for a battery which had a special
>reserve (almost like a second battery within a battery) capability.

This type of battery was available at a cheesy chain store called Canadian 
Tire Corp, here in Canada. They kept price cutting to dump them, eventually 
at half price they still didn't move much. Haven't seen them since, so I 
think mebbe they suck! CTC has sold me batteries that they knew were 
defective, discontinued because of that, but still available as stock. They 
would still be selling the backup battery you mentioned if they could make 
money, so I suspect you really don't want to buy one of those.
        In a '71 you can fit the biggest damn battery you can find, so go to 
Sears and buy the newest biggest DieHard Gold you can find, great warranty 
on them too! They do make a real VW van sized one, mandatory for Vanagons, 
but you can get a much more powerful one for Ramona. They are all the same 
price here BTW, around $100CDN, regardless of size, figure that one. Other 
good battery was from Interstate, rec'd by several listmembers.  tim s.