Longest battle I've ever seen: Fun story, an entire BP team versus a shedinja. Only Espeon had attacks and shedinja had more PP than it so the player just switched back and forth to stall out PP. Considering insane PP on BP team and the determination of the losing player to win, it took a long time, probably 1k+
My longest battle (I think) was this horrible match between a weezing (with pain split) and a resttalk throh- it ended at 183 turns, IIRC.
I suppose that, discounting status/harvest leppa berry shenanigans, the theoretical maximum would be with every pokemon knowing 64 pp moves that don't deal damage and using leftovers, in which case you could hit 1536 total active turns before your pokemon would start struggling, adding another 30 to the total. This doesn't count turns switching out, since as with para/confusion hax, that would make the battle limited by your power company and not much else. Though who would subject themselves to such a thing, I can't say. 183 turns was grueling in its own right.
Is there a maximum of turns in Showdown, a theoric limit that stops the battle for going on for days with Leppa Berry/Harvest shenanigans? If not, I'd totally wait for someone making a timer on a website with a battle continuously going on with scripts. "5000 turns!"
In theory, you could have an infinitely long battle even without the use of Leppa Harvest because both players could just keep switching back and forth repeatedly. Leppa Harvest would make it a bit more interesting though :I
My longest was a 208 turn game on Pokemon Lab, in DPP NU. It was either against Closet, Crona, or Corn. (The latter two don't really sign into PS anymore afaik) Anyway I remember that it was my Quagsire and Shuckle against an opponent's Shuckle and I won the PP Stall war. One of my most memorable matches as I remember there was some pretty funny commentary since a lot of people joined the battle.
I have a new longest battle--it was just a little while ago, but it was 129 turns. It was against a PP-Stall and Baton Pass team. It was quite good too, but needed more of an offensive presence to build off of the ground it gained. Not much, but a little more would have helped.
I'm actually watching a battle now between an Exeggutor that works like a Funbro paired with Entrainment Durant. They are currently on turn 396 and neither side has lost a Pokemon. I don't see an end. ._.
I think my best took 119 turns... to get the first KO! (after that it was a forfeit, so idk how long it would have gone on for)
It was fifth gen ubers. Pretty quickly during the battle, it came down to my Latias vs. his Lugia; I was running Substitute/Calm Mind/Dragon Pulse/Roost with a physically defensive EV Spread (and soul dew, ofc) and so I figured I might be able to set up a sub if he was running Dragon Tail > Whirlwind. Unfortunately, he was an offensive Calm Mind Lugia, with 3 attacks and recover. We both got up to +6, and neither of us could switch and forfeit the boosts, since the other pokemon would sweep our team. When we were both down to just our recovery moves, I was able to switch out into a set up sweeper, but it was fun to continually use my Latias to check his Kyogre until I killed it with its own struggle damage. I forget what happened with the rest of it, but I remember the first KO came on turn 119.
Simulator wise: I think my longest battle was on PO at about 200~ or Shoddy Battle in gen 4 at around 230.
Otherwise, I think my longest battle of all time was while playing a Pokemon MMO. The battle--I swear on everything--took over 2 hours to complete. This was during a Guild War with a player named Latias. Her team was a pretty well trained (you had to catch train all of your Pokemon) stall team while I ran a more balanced offensive team. The problem was the fact that items were able to be used....and we both had a shit-ton of Full Restores. I think I ended up losing that battle but it was probably one of the best battles I've ever had in my entire life!
I had a 2,000 long battle before, it was sun stall vs sun stall Ubers,my subtoxic ho-oh vs a sub3 attacks heatran, neither of us could break each others subs with 1 shit and by that point it was already 1,300 turns so we stalled out 700 more to finally get to the end of it