For what it's worth........I refill the 1 lb portable tanks from my 22 lb tanks using a special connector purchased from Tractor Supply. I'm sure other places have them.
To get a full charge, I put the 1 lb tanks in my freezer overnight. I find that inverting the 22 lb tank, connecting the 1 lb tank then opening the valve is best. The pressures will automatically equalize, thus no issues with overfilling the 1 lb tank. When it stops hissing, turn off the valve and remove the 1 lb tank.