I did a little more thinking about the quick battle rules while I should have been working today. I think the system is chiefly lacking rules for three things:
3. Skill of the general
So I propose the following additions:
Before the battle assuming both sides are marching, each side rolls a d6. On a roll of 1 or 2, that side is surprised. It suffers -2 to its first battle round roll, and -1 thereafter. If one side is static, it is only surprised on a 1. It is possible for both sides to be surprised, in which case the modifier may be disregarded.
The weather modifies battle rolls as follows:
Very hot and dry - if one side is static it is never surprised. If both sides are marching, each side is surprised only on a 1.
Rain or snow - the ordinary bonus for mounted troops does not apply.
Heavy rain or snow - the ordinary bonuses for mounted troops and archers do not apply.
Fog - if one side is static and the other is marching, the marching side is surprised on a 1-4. Either side may flee at any time and automatically evade pursuit.
Skill of the general
A particularly skilful general gives a +1 bonus.