For those of us who like tools, Harbor Freight has a battery tester I got for less than $20 on sale, not sure the normal price, that will test a battery under load. It is a volt meter with a BIG resister. The switch to engage the load is momentary and the unit gets hot as the resister disapates something like 100A for a few seconds while you get a reading. I bought it to test an old boat battery. Seems to work fine. The scale it has reads in simple green and red terms and also CCA. It also will tell you if a battery is fully charged (that doesn't require a load, it is just voltage). I found my battery, despite being more than 10 years old, is fine. Here's a link:
One word of caution, I do not buy from Harbor Freight mail order. I've tried it a couple times and waited a month or more for something to arrive. They are VERY slow. There is a store nearby and I buy there.
128i Convertible, MT, Alpine White, Black Top, Taupe Leatherette, Walnut, Sport
Ordered 5/22/09, Completed 6/4/09, At Port 6/9/09, On the Georgia Highway 6/13/09, Ship Arrived Charleston 6/24/09 at 10pm, PCD 7/21/09