>>274771218
Vendor battery seems to just be for speedrunning(?) because you run into so many of them.
Shitty screenshot but the last floor of the tower had a second vending machine where you could buy pieces of the gravity gun for about 12000 ammo each.
For nearly 100,000 ammo, you can have the gravity gun [spoiler]on one of the shortest levels in the game with the least amount of combat[/spoiler]