you can use those refill bottles from the parts stores. they work, yes its that easy screw it on the line push the button, fill till its in the green on the gauge on the can. done.

but being your low now, it leaked out, so it wont last forever. maybe a week, maybe till next year. in the end, you want to find the leak and fix it, or your dumping 30 bucks a can into it all the time maybe.