Didn't say it was exclusively about signs, but that was the topic when cordless tools were brought up in the thread. My point was just that when it comes to sign installs, or removals, for that matter, cordless tools can basically hang with corded tools. There are obviously advantages and disadvantages to both.
You basically changed the subject when you brought production work into the discussion. If we're talking about all day production work, then corded may be better for you.
That being said, I wouldn't use 4ah batteries for what you described anyway. 4ah batteries aren't intended for what you're describing, they're for light duty work. I'd use 6ah, 9ah or 12ah 60v batteries and, at the risk of ruffling your feathers, I think you'd be surprised at what they can do...including driving 5/16" self tappers through wood and steel.
By way of example, a little while back I helped a friend install a couple of hundred seats in an auditorium. Each seat was attached to the concrete slab with four 1/4" x 3" wedge anchors. He had a corded Hilti SDS, I had the cordless DeWalt SDS. We started on opposite sides and worked towards each other. When he finished, I had eight holes/two chairs left to go. So each drilled right around 400 1/4" x 3" holes. I used a total of three batteries.