here's a fantastic webpagefor everyone to look at. all about car batteries.

http://www.geocities.com/bjb_darden/carfaq.htm
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Kenric Tam
1990 Volvo 740 base sedan (B230F)
My Volvo 'Project'

Everything the previous posters said was great, though I myself have always used vaseline rather than anti-corrosion spray. Get the felt washers impregnated with anti-corrosive at K-Mart or an autoparts store, and slip them over the greased terminals. They're cheap, and the green/red colors provide a quick read on which terminals are which if jump starting with cables--red obviously goes on the positive. These usually have a push out center for fitting larger diameter terminals. Regarding the first poster's advice to check your battery's water, assuming the battery is refillable and not the sealed type, be sure to fill only to the mark, usually a little internal "collar" about 3/4" down the throat of each cell. Rather than pouring, I run a 2' length of slender windshield washer tubing down through the handle of my distilled water jug, then siphon into each cell as needed. Once the siphon starts, you move from one cell to the next, pinching off the tube to stop. The water in the cell will "wink" as it reaches the stop collar. A flashlight helps to see this. Use ONLY distilled water, as the lime in tap water can eventually damage the battery.

scrape off corrosion with metal brush. Spray nicely cleaned battery terminal and connecting wire(s) with a battery corrosion preventative spray. I use permatex (I think thats what the company is) and it works fine. Make sure your battery has water as well. And, as Steve said, get new terminal washers. Don't let any of the corrosion stay in the car either; vacuum that shit up, or it may corrode something else...

Roguls
New York, USA

Exactly what Steve said - I do this for my cars and boat always. Heinz

It's actually in the "starting" section. Anyway, you can clean them safely by:

-Disconnecting both cables and keeping them clear of the battery
-Mixing a baking soda solution in water
-Wiping that on the surface of the battery and on the connectors, then rinsing (this removes acid). Rinse the tray as well.
-Cleaning grease off with rubbing alcohol and a rag
-Polishing up the posts with either fine sandpaper or a metal brush
-Cleaning the terminals with a metal brush and fine sandpaper
-Inspecting them and the cables for damage, broken strands, etc. Replace if needed.
-Reassembling with the little red and green battery anti-corrosion washers (they really work!) under the terminals and then, once the cables are secured, spray the post, connector and exposed part of the cable with anti-corrosion spray (a red lacquer you can buy in the battery section at KMart, Walmart, etc.)

Your biggest problem will be corrosion damage inside the cable, which is tough to fix.