KTo purge air from my grease guns, I open the lever all the way, firmly hold the end of the barrel, then swing downward like I'm hitting a golf ball as far as I can, but in both directions; this forces grease towards the pump and squeezes the air bubble to the rear-end of the tube.
I've used that technique ever since dad taught it to me when I was old enough to use a grease gun, it has never failed.
There is a distinct advantage to using a battery-powered grease gun, especially when greasing hard to reach zerks. Nearly all hard to reach zerks require 3 hands, especially when you have a flexible hose on the a manual gun.
I use my battery gun so infrequently the battery is always run-down, so I have to anticipate and put the battery in the charger the night before I need the gun.
Anyone else have a designated charging station in your garage?