Funny, my own experience is that I found the cavalry to be quite underwhelming - unless you micromanage every single charge-retreat-charge, which quickly becomes impossible for me once there is more than fifteen units in each side of the battle.
The charge is painful to manage, and outside of the "artificial" charge, cav tends to die very quickly.

Now, if you want to slow down the pace of battles, there is an easy fix : just open the export_descr_unit.txt file, and halve the first number in all the stat_pri and stat_sec lines. It will drastically diminish the killing power of all units, and make the battle much longer (I would recommand to double or triple the amount of ammunition to make up for their reduced effectiveness if you don't want to have completely useless archery units though).