I've never used a battery model but I have an air model. It is [censored] awesome. If you have any zerks that don't take grease well, it easily pumps the grease in. Maybe I'm lazy but it sure makes greasing equipment easy.
don't bother with a 12V gun unless you just want to be made angry. the 14V Lincoln is a [censored] handy piece of kit. I have one for greasing my crane's and forklifts.
I also have a pneumatic grease gun that recently gave up the ghost.