Ok, I figured I'd do the same. My grease gun has also worked perfectly, but I haven't kept track of how many tubes of grease I can run between charges. I'll admit at first I didn't think it'd work very well, but it works great. If I was to guess, it'd probably do close to three tubes between charges.
Here's a tip I learned from a mechanic for bleeding grease guns. Hopefully this will make sense and I know it works well with Lincon manual and battery operated guns. Pull the plunger out and lock it in place. Then unscrew the tube from the pump and remove the old cartridge. Take the plastic cover off a new tube of grease and insert it in the gun tub first. Then pull the metal cover off the end of the grease tub and start threading it into the pump. Don't screw it in all the way, but leave it pretty loose. Then unlock the plunger and spring pressure will push air out through the threads. Then at the same time, start pumping grease and slowly screwing the tub all the way in. If done right, you'll start getting grease after 4 or 5 pumps and the air is completely purged. I usually stick the end of the hose in a small can or garbage can because I usually pump 2 or 3 shots of grease out before I'm done.
I've gone through a box of tubes using this method and I haven't had to crack the pump vent once. This works great and it only takes a minute, two at the most to change a tube. I'm sure many of you all ready know this, but lets just say I used to use other methods for changing tubes of grease before someone showed me an easier way:Banghead Hopefully this will help someone