Do repairing Vax has to be so tedious? My engineer has level 4 of mechanical repairs and she repairs only 3 points per skill use (with 100% success). Multiply this by the time that using the skill takes and... I really don't have all day to play the game.

Why can't the game determine the success rate by comparing the damage Vax has taken to repair skill of a PC, and the success would result in a full repair? This I think would not only make sense (a poor mechanic cannot repair a severe damage) but also, what is more important to me, would save a lot of real life time.

I think you are supposed to be able to upgrade him but I wasn't able to keep him alive long enough before he died and it had been too much hassle to keep him alive and so I moved on without him, damn robots anyway! Next play-through I will definitely keep him alive all the way through, as well as a couple other of the random followers.

I'm in L.A. now and Vax is doing a fairly good job when shooting at highly armoured opponents. Keeping him alive is another matter though - the follower's AI is incredibly silly. One thing to remember that might help in it is that the follower will always follow a character you had selected as a lead when you saved the game. If you load this saved game, he will stick to that person. I usually make Vax follow my mechanic, so she can quickly repair him in case he gets shot.
I didn't find any opportunity to upgrade Vax yet, apart of overclocking him temporarily with a science skill in order to make him shoot three times during each of his turns.

Out of curiosity, have you ever recruited Vax in Wasteland 1?

Me? Well, I only played Wasteland up to some point before I had to drop it, so I don't believe I had a chance to recruit him. But Wasteland 2 gives some clues about his origin, or rather the origin of robots in general - Base Conchise. Also, I read in a Wiki that in W1 he had to be assembled by the player.

The question is: is he upgradeable? I find lots of parts in the remains of robots, synths and turrets. It would be fun to boost Vax with them in some way.

I don't know about Wasteland 2, but in Wasteland 1, he is treated like any other recruit. This means that you can level him up, teach him new skills at the library (if you raised Intelligence), heal him with Medic or Doctor if he's injured, clone him, and send him off alone across the wilderness. He just starts with really good stats and (IIRC) 10 ranks in Toaster Repair.

I'm not sure, but Vax is another robot than the playable one, the playabe is called Vax and is found in Las Vegas sewer (There is a book in the Wasteland 2 citadel about this location).

Vax is mentioned in the short novels that come with the Wasteland 2 as another robot found inside of the Cochise Base, but I don't remember finding him in my playtthrough of Wasteland 1 (Of course, I was trying to survive so didn't explore too much that base)

And I had never found any dialogue in W2 about upgrading robots, maybe the confusion is the fact you can orvercharge them with the repair skill.

Pd. yeah, the wiki say Vax is the only playable, probably Vax is there for the chances (very, VERY high) to lost someone in your initial approach to the base. Sad, because you find him in the end, and Max at middle.