This is unrealistic behavior IMHO and ruins battles that last over one day.
I suspect the multi-day battle code isn't quite finished. As far as I understand it, you should be getting units back, pretty much everyone who has left the field, and some portion of your wounded and missing. This includes a lot of artillery. The only troops permanently lost are those killed and captured.
Some wounded would be able to return to battle the next day, and a lot of missing will show up overnight. Units might be at a lower strength, but they always returned to battle within a day or two. If necessary, units would be reorganized, with very small units combined to form a normal sized unit.
Hook