I have the 20v Lincoln poweluber here, had a 14v version up to last year, but sent that one into the quarry!!! One of my favourite tools of all time, no bother greasing any bearing or uj. Each stroke provides about half the volume of a stroke of a normal grease gun in low speed, so is easily controllable. There is a little plunger under your thumb that moves with every stroke, so you can count the pumps even when in noisy environments. 2 speeds on my gun, but I rarely use the high speed. Comes standard with a really long, ultra flexible hose, so you can easily grease nipples where you wouldn't be able to with a standard gun. Also far more powerful than any hand operated gun, I've used mine to unblock grease nipples that couldn't be greased. It enters a special pulsation mode when it encounters a blocked nipple, and 9 times out of 10 it will free it.
Really couldn't recommend one highly enough.