My longest battle without a time limit was when I was the Aragonese against the French, fighting just outside Paris, their penultimate city. I had my Grand Host, which I always call my best or main army, with the most up-to-date troops and such. The French had basically all their troops left in the world on this field outside Paris, ready to defend their capital. The ration was about 1500 on my side, to 3400 on the French. But my troops were better, on the whole.
I had a few trebuchets, so I peppered their armies until they launched an attack. All 3 of their stacks smashed into me, I had dismounted Armats holding them off and taking huge casualties, and my left wing nearly buckled under the enemy knights. My right wing beat back their spearmen, though, and swept round to hit the left wing attackers, routing most of their infantry. I thought I'd won, but I looked at the ratio bar and it showed still about half and half...I checked the map and saw a huge army of mounted cavalry charging across the plains towards me, and I only had 2 units of cavalry and my general.
My trebs managed to take down about a unit or two with flaming ammo, then I sent my general and the nights charging out to meet them, with my infantry lining up in formation behind. The cavalry engaged and held up their charge, meaning my infantry could join the fight and take down the enemy from behind, routing them, even though my general and most of the cavalry sacrificed themselves. In the end, the battle took 2 hours-ish, it was epic. I then besieged Paris with the remnants of my army but got beaten back by a HRE sack allied to the French.
