IMHO, it was the right one if it has a red top.  Price and possibly
guarantee does vary a little depending on retailer.  There are only 3
red top models, 6V and two 12V.  The 12V models are the same except
for presence of GM side terminals or not.  The "private labeled" ones
are the same.  I'd be suprised if you would need the warranty--they're
pretty bulletproof and are apparently extensively used in industry.