Just one of my favorite scrap runs that yielded way more than it should have.

Working in the laboratory equipment refurbishment field, we come across so many battery backups and those same style lead acid batteries are used in various equipment as well such as Low temperature freezers (-90 Celsius or so).

The local yard close to where I work for whatever reason doesn't take lead acid batteries so instead I get the fun of taking every single one home. Once a year or so I take anywhere from 50-100 batteries.

With the pretext out of the way, I roll into the yard that in the past has treated me the best with the best pricing. (we have 3 within 15 minutes of my house) Generally batteries these small go by the pound but this day the guy that normally works the precious metal scale was out for the day and the guy that filled in for him was too new to know how things were done. So he gave me the full price of per battery instead of per pound.

Once I got in my truck I saw the number "84" written down and I was furious. How the heck could all those batteries possibly only weigh 84 pounds? I walked into the office to get paid and told the guy "I had a whole lot of batteries to only be considered 84 pounds." He assured me that they do the batteries as count and not pounds. This guy has worked there for at least 11 years when I first went there so when I told him they were just smaller battery backup sized batteries, I figured he would know that it should be by pound and not count. All he had to say back to that was "they're lead acid, right?" when I said yeah he said I was good and its by the count.

The next time I went it was by weight and the same guy in the office rang up lead acid batteries by weight. I still don't understand. But I think batteries were about 8 bucks a piece at that time so it was an amazing pay day that I'll never forget.

I also once dropped an iron engine block off at this same yard only to find out they don't do any categories of iron/steel. It all goes as the same. I became a lot less sour about that one after this.

Anyone else have anything similar happen with their scrap adventures?

Sounds like you benefitted from a combination of Human error and a glitch in the matrix that was remedied after your visit when they realized their mistake.
We used to have a yard that bought car/truck sized lead acid batteries by the piece at $10 bucks (this was maybe 2006-2008) but they folded a few years after being operational. We get a ton of UPS battery backups as well, being in the electronics recycling field, so when we have nothing else to do, we will tear them town and pile them up on a pallet to bring in, but the pricing there isn't anything to write home about.
There is a yard near me (we also have 4 or 5 yards within 10 minutes of my house) that is cool about letting me fish out computers and servers that get tossed into the tin pile (happens all the time) and they just deduct it from the weight of stuff dropped off. Easy enough math if I'm also dropping off tin and I'll gladly pay 8 cents per pound for computers, even though I normally get them for nothing.
As far as cool stories go, aside from the occasional tool or computer, nothing too crazy.
I find that if there is a giant winfall of cash, or something crazy gets dropped off that you can nab, it's usually on the backend of an inexperienced person not knowing enough, whether it's a worker or someone new off the street, which is why these types of forums are important.
In your scenario, sounds like the guy knew what he was doing and there was a communications breakdown in your favor.

It's almost always inexperience, you would be correct on that. One of our yards just constantly has people roaming it looking for the good stuff. It's quite obnoxious as they'll come over to your truck without saying anything and just peer around at your stuff. Most don't do that but the few that do need to learn personal boundaries. So I've never bothered with looking around for goodies. Although not a bad idea at all.

I did however once find some zero gravity lawn chairs that walmart threw in the scrap because they rusted in storage over a winter. Lasted several years for a couple bucks a piece.

Otherwise I barely scrap anything anymore. I used to be so big about it but nowadays it's just for the purpose of not throwing it away or having a couple bucks to buy that tool I've been thinking about but couldn't justify.

New yard opened near me several years ago. Most of the employees were experienced, but the combination of a carless yard man and a new payclerk erred in my favor.
I had taken 300 pounds of cast iron, which at that time was about 5 cents per pound. The scale operator wrote it up as
Cast". At the pay window, the new office person didn't know of the different "cast", so she cut my check at the 60 cents per pound of cast aluminum. Sure was a shocker to see a fifteen dollar load paid out at $180.
I refused the check and asked her to confirm with the other worker the price of "cast iron', not cast aluminum. I like free money, but not at someone elses expense or error. In addition, business cease to exist in a convenient location if such errors compound. So did I lose $165 dollars by being honest? maybe you could think so by that one time. But...
Soon there after the owner gave me a tractor trailer full of computer scrap to recycle, at no charge and then sent three more trailers full directly to my house so I could work them up with the only stipulation that I sell the metal back to him, and dispose of the boards elsewhere I wished, since he did not buy them, plus gave me carte blanche to salvage anything that caught my eye in the yard, and didn't even have to weigh it out.

Karma, if you believe in that sort of thing.
It's true what they say: what goes around does indeed come around.

I try to be as honest as I can with people especially cashiers who if they mess up will get reprimanded since the drawers are usually counted daily. But like with telling the guy the batteries weren't right, I assumed maybe they had been doing it wrong all the previous times and this was the one right time. I left out that the guy who helped unload had to go in the office and ask the guy after I said they go by weight and then still got it wrong so I felt as though I did all I could.

That same yard seems to change things constantly but they're good people none the less. I doubt anyone ended up even noticing or losing their job over that mishap. I also *believe* the guy behind the counter is the owner but I'm not entirely sure on that.

I agree you did right by calling their attention to the ticket, but once they "confirmed" and were unwilling to change it, the overpayment was yours. I assume their not pressing repayment after their mistake was discovered was from embarrassment