A portable air tank like the 5 gal is OK, but I'll often use a 10 gal, enough air to top up all tires.
These tanks are only effective at transferring air when they are well above the tire you're filling.
A tank depleted to 40PSI is very slow when trying to get a 25PSI tire up to 32PSI, etc.
Surprise: The large fitting on the tank typically has an ID for air that's only
i/8" !!! So it fills and discharges air way slower even under ideal conditions!
If found that out a few years ago where I ripped off the old fittings and fitted a T fitting
and 'M type' QCs so I can put a storage tank it inline with my air line and close to my impact
wrench for suspension work, ie, to make sure there's lots of air when cranking hard on the wrench.