You don't need acid, sodium carbonate (washing soda) will do fine if not better. It will not attack metal surfaces, just rust. Also, don't use a battery, use a dumb battery charger (with the ammeter, without the control circuitry).
Here's a good summary:
http://www.stovebolt.com/techtips/ru..._derusting.htm
Avoid stainess electrodes, as chromium salts are extremely toxic, leaving you with several gallons of toxic waste. It's unclear whether the chromium dissolves, but better safe than sorry. Sacrificial mild steel anodes do the job just fine, just need replacing after a lot of use.