What's Reserve Capacity, and how's it different from A⋅h?

Question

My 1J0 915 105 AD OEM battery from a 2008 Jetta 2.5L SE is noted as having the capacity of 61 Ah, the only marking on the battery are as follows:

e ENERTEC
EMC
1J0 915 105 AD
12V 61 Ah 330A DIN
540A EN/SAE

When I go to InterstateBatteries.com, which is claimed to be the number 1 retailer of aftermarket batteries in the United States, and search jetta, then see nothing, yet presented with the option to narrow down to Automotive, 2008, Volkswagen, Jetta, L5/2.5L, - (have no idea what the "-" option is for, the other option was "54") -- seven pageloads later after typing "jetta" -- none of the batteries presented are specified to have any sort of A⋅h ratings, yet they all appear to come with a ReverseCapacity-25 specification.

How does A⋅h and ReverseCapacity-25 compare?

• Is 61 A⋅h at all equivalent to 61 A⋅h ÷ 25A = 2.44 h, which is 146.4 minutes of reserve capacity, or is there some other trick?

For what it's worth, all of these Interstate batteries appear to have a higher CCA ratings than OEM's 540A, yet all of them at the same time had at most 130 rating for ReserveCapacity-25.

• Why does Interstate only have batteries with 95, 115 and 130 RC for my car, yet they all have between 610 and 790 CCA ratings (OEM's 540A)? Doesn't 95 RC mean only 95/60 * 25 = 39.58 Ah?

Answer 1

I think you may be seriously overthinking this purchase. Simply get the correct size battery for your car. The CCA are a ballpark number whose truthiness is going to be dependent on the honesty of the manufacturer.

Reserve capacity is the number of minutes a battery can output a useful voltage under a 25 Amp discharge load. Since a specification is going to be a minimum-spec met for the battery, aka meet-or-exceed standard, it simply states that they all meet this standard- however many minutes the standard may require.