I've fought in several multi day battles and the basics were the same. Whatever happened on day one MUST affect whatever happens of day 2, 3 or 4.
Your troops fought for a day, night was called.
You were now given chances to rally, resupply and refit the units, some movemnet around teh battlefield and its environs was allowed. No further towards the enemy but slight readjustments of position.
For day two the units which had really fought – as in discharged thier weapons and taken casualties for at least 4 combat turns the previous day – were adjudged fatigues and where given penalties on anything to do with offense but not defense.
Even if they were shot to pieces they could still be used. Of course many of the shot up or partially rallied units from the previous day had been folded into combined units, brigaded. Thier morale was adjusted down to the that of the lower unit in the brigade.
You or your oppponent could have used the cover of night to withdraw, but in doing so some units may become disrupted, suffer desertions, get lost etc. Leaving your opponent with the battlefield and a bunch of loot.
When doing multi day battles it's always good to spend time figuring out what actually happenend in the night. This includes recovery of routing and pursuing units as well as resupply from own or enemy resources, movement of units, where are and what do your scouts actually see etc.