We have 2 12 volt Milwaukee guns and an 18 volt DeWalt, and someplace is an old blue Lincoln.  I think the Lincoln was designed by a grease company because it inevitably wasted half the grease we put in it.  We've had almost no trouble with the Milwaukee or DeWalt guns.

On a side note we always store out grease tubes standing up. I have an old milk crate I throw in the Mule servicing irrigators with spare grease, oil, etc in it and we wired the bottom of a plastic bottle in the corner to keep the grease upright.  Almost never have a priming problem with any gun, electric or manual.