2003 Audi A4 Check alternator and battery type

Using your ohm meter on the 20 or 50 volt DC scale and the engine at a warm idle, all accessories "off", test accross the poles of the battery. Your meter should read between 12.5 and 14.5 volts. If your meter is within this range, the alternator is charging like it should. If below 12.5 it's not charging. If it's above 14.5, the alternator/regulator is bad and it will "cook" your battery.
To check amp output, add the load of the accessories ie; blower on high, headlights, AC and the voltage should not drop below 12.5 volts.
On what batteries will fit the car? We don't have that information in our data base, BUT, any store that sells batteries wil have a listing of the different sizes that will fit your car. I've always, living in the midwest, put in the heaviest battery that would ft. Hope this helps.