I looked into the on board air system and said the heck with that....I still use the CO2 bottles.

Any compressed air works. I use oxygen bottle to fill o2 bottle. Bought a coupler off ebay for 30 bucks or so. I drop bottle in freezer for day or so.. Connect bottles open o2 bottle then slowly open larger oxygen bottle. Close both diconnect and good to go. Chilling just gets more into bottle.

I carry a argon bottle on trailer for tig welder and can fill with that if need.