Battery terminology

"The definition of the Cold-Cranking Amperage (CCA) of an automotive battery is the amount of current a given battery can deliver for 30 seconds at zero (0) degrees F without dropping below a specified cutoff voltage (manufacturer-specific, but usually 10.5 volts)."

"The Amp Hour rating tells you how much amperage is available when discharged evenly over a 20 hour period. The amp hour rating is cumulative, so in order to know how many constant amps the battery will output for 20 hours, you have to divide the amp hour rating by 20. Example: If a battery has an amp hour rating of 75, dividing by 20 = 3.75. Such a battery can carry a 3.75 amp load for 20 hours before dropping to 10.5 volts. (10.5 volts is the fully discharged level, at which point the battery needs to be recharged.) A battery with an amp hour rating of 55 will carry a 2.75 amp load for 20 hours before dropping to 10.5 volts."

Source: Yahoo Answers

 

Good question. I've come up against this problem in the past and perhaps I can try to offer a likely answer.

Ah vs CCA
My understanding is Ah and CCA are completely different measures of a starter battery's capacity. Ah rates the overall capacity of a battery while CCA rates how much of a battery's current capacity it can deliver at 0°F over 30 seconds. A similar rating called the CA (cranking amps) or MCA (marine cranking amps) rates a battery's current capacity it can deliver at 32°F (0°C) over 30 seconds.

You could say Ah measures how much capacity a battery can have when fully charged while CCA tells you how much of that battery's capacity (when fully charged) can be delivered at 0°F (-18°C) over 30 seconds. Intuitively, for car starting applications, the CCA rating is more useful to have because engine-starting efforts are very brief and requires high amperage while Ah ratings are more useful if you need to consider steady state continuous discharge of a fully-charged battery which is no longer being recharged, which is not the case for a car battery.

IMO, the Ah rating is a pretty useless battery rating for a car that has a fully-functioning battery charging system. Ah is more useful for gauging capacity for batteries in your phone or AA/AAA batteries powering your gadgets.

European "Amperes", A(EN)"
As for the European "Ampere" rating my suspicion is that it tries to provide the same sort of measure as CCA and CA/MCA.

I have noticed Bosch batteries in Europe are rated for both Ah and something called A(EN) with absolutely no explanation of what A(EN) means (while Ah is an internationally agreed-upon unit). The A(EN) ratings for Bosch batteries also appear to coincide with CA ratings of North American batteries of similar size. At the same time I located indirect references to what A(EN) may actually mean... Amperes (European Norm)? Given that Europe uses SI units (metric), I suspect the A(EN) measure is in fact a European CA/MCA unit of measure... 30 seconds of current at 0°C.

In your example, the 800 CCA Interstate battery would translate to 1088 CA/MCA which is very close to the 1000 "ampere" rating if you assume a rounded off rating to account for possibly slightly different lab testing methodology between NA and European lab standards.

I also suspect the reason for the very confusing European measure of "Ampere" is a stop-gap attempt at mutual turf protection, to prevent consumers from buying cheaper products across the pond given the open markets available from Internet commerce. IMO, the battery business is highly geographically controlled by local stakeholders. Turf protection.

Perhaps a true battery expert can chime in.