I would go with a quality manual pump. Pay the extra money and get a USA name brand. These last a lifetime, batteries don't. Maybe a air driven; again name brand. Jeff
I was one of those who swore by a manual greaser for the first 10 years of dealer work. Another tech at the time came in with a Husky pneumatic grease gun and did a full service on, IIRC, an L48-which as you know has a TON of fittings on it (FEL, BH, etc). Took him maybe 5 minutes to grease all of them, and it takes me 30 minutes to hit 'em all with the manual. I was sold on it. Bought a Lincoln pneumatic grease gun from the tool truck the very next day. That was 16 years ago and thousands of tractors, and the grease gun still works perfect to this day.
That said.....
Some of the other brands aren't quite as good. The Husky in question had to have 2 modifications. One was that the grease seal on the cartridge piston failed and on a hot day, the contents of the grease cartridge would end up on the wrong side of the piston, creating a big mess when you changed the cartridge. New seal fixed it. Also, it's really slow in comparison to the Lincoln. It works and it's easy to use but it's slow in factory configuration. IF you take the head apart, you'll find the vent hole. Air vents out of this hole. It's too small. We came up with the idea to open it up as far as we could without compromising strength of the head, which I think was around 1/4". The original hole is about half that size. After that, the speed increased drastically. Still not as fast as the lincoln but close. One thing I didn't like about the Husky was that it is tough to bleed if it gets air in it, but that's not often. Usually he'd pull on the T-handle to see how much was in the gun, if it didn't pull out much (or not at all which was often since several of us used it....), just change the cartridge. If you run it dry, it'll get air in it. Usually you could bleed it by screwing the gun back together just a thread or two, then pulling the trigger while you're screwing it back on. Worked about 80% of the time. Sometimes you had to bleed it which was a messy ordeal. The Lincoln is self-bleeding. I really like it.
I'm not sure I'd like a cordless. Sure the lack of a hose is nice but that battery. I have 2 cordless drills and it never fails, I grab either the drill or the driver to use it, always in a bind at the worst possible moment, and the battery is always dead. And worse, the other 3 are also seemingly dead. So you have to stop what you're doing and recharge. With pneumatic, if you have shop air, you have a working Lincoln grease gun.
One thing most don't think about when greasing. New grease also flushes the old stuff out, which may contain dirt, water, whatever. On a FEL and BH I always do the flush routine. It's messy but I've never had a single pin or bushing wear out. Doing this requires a LOT of manual pumps. If you have a pistol grip manual greaser, your forearm will look like popeye in no time. If you have a lever type, you will wear yourself out in about 4 or 5 fittings.
