If your using a car battery or deep cycle for power I usually install some type of resistor to control the power also. I've removed rust from lots of stuff with Electrolysis and it works great, but I never hook the battery direct without controlling the power.
A light works well. Using a tail light bulb or such, the bulb limits the amount of power to the tank. If say the bulb is 36watt that would be 3amps at 12V. If you want 6amps use a larger bulb, or 2 36watt side by side.
I forget the watts on the bulbs now, and I had some other types I used.
You can also use normal incandescent house light bulbs, a 60 watt at 12v should give you about 5amps to the parts tank.
Using a charger on the battery, adjust charge amps to the tank amps, and it should maintain a full charge on the battery, so say set both to 6amps.
You know with a good heavy battery and cable you can make a stick welder using a direct short at the rod! I don't want that in my tanks if somehow my cathode and anodes touch. With smaller wire you can make an electric heater, until the wire burns in 2 LOL
One of the reasons I control power from the battery as well as other reasons.
Also keep an eye on your water level and vent well. Basically your doing the same thing as making a hydrogen gas unit, breaking down water to oxygen and hydrogen gases is done the same way.
I was using 35 and 55 gal barrels for stuff for awhile. It was fun to make a little hot air balloon and vent the gasses to it, then after awhile watch it just lift up and float away as it filled with hydrogen. LOL