I may not have bought a "light purpose" battery however the euphemism for that in the battery trade is "general purpose", using zinc carbon chemistry.
As for the ratings of batteries, yes they should publish the capacity of their batteries. Some manufacturers selectively release some of that information on their website. For instance, the Eveready 1215 "Eveready Super Heavy Duty AA 1.5 V" carbon zinc battery, which relies on Zinc-Manganese Dioxide (Zn/MnO_2) chemistry, has a capacity of 1,100 mAh to 0.8 volts (Rated capacity at 25 mA continuous at 21ºC) according to it's data sheet.
http://www.eveready.com/batteries/Pages/super-heavy-duty.aspx
http://data.energizer.com/PDFs/1215.pdf
Don't know if this really relieves you of your concern, but it's interesting to know and probably remarkably similar to other "Super Heavy Duty" batteries on the market.
