What I need to know is:
1) Would it be one giant battle or skirmishes.
As this is the first war and the leader relatively low level I'd say that the battle is infact a series of skirmishes with each small band working idependently of others, very little coordination but all driven by their individual zeal.
Make lots of Will checks for Morale. In this case I'd also say that the Side with the giants has the advantage. HOWEVER if the opposing side can take out one of the giants then this will be a huge morale boost for them and a morale dampening for their enemy. (who must all make a morale check with a -something penalty.
2) Death rate before someone withdraws
Very low. In many small scale societies battles were sometimes determined by combat of champions - ie two chosen champions would fight and the winner of that contest would win the whole battle.
In fact sometimes (in my culture) whole battles could be won simply by the best war dance (maxed out Perform skill no doubt
) with no deaths at all
- see also the beginning of the Shaka Zulu movie for an idea of how small scale skirmishes were sometimes dealt with (in this both sides throw light spears which rarely kill but can draw blood - first blood wins)
Other options include killing the leader (at which the troops break and run (in your scenario killing the giants should do the same thing) - see David and Goliath on this point
3) Would it last hours or days?
Usually Hours, sometimes days NEVER more than two Weeks at a time.
Again small scale socieities rely on warriors who are also farmers and need to be out tending crops or hunting/fishing. Again in my culture war was possible for only two months each year (in summer between planting and harvest time)
If the society has professional soldiers then it can be out for much longer (but then they would have the advantage in your case anyway)
My Rationales
Okay from my own culture which was tribal
- each 'clan' has an idependent leader and fights as a 'squad'. The overall 'general' must lead by exaple and force of personality (and is often ignored)
Clans fight for 'personal' (clan) glory in the first instance, and maybe from some higher zealotry. Overall morale however is low and individual clans will pull out and go home at a whim.
(My wifes great-great grandfather was involved in battle against British troops back in the late 1800s. It is reported that he saw the size of the British army and that his side was losing and so up and went home (after which he converted to Christianity)
I know that a similar situation applied to Japanese armies - they were lead by individual daiyamo with varying levels of loyalty and morale who might abandon the war at whim.
I suspect the same applied to Medieval European armies (who were often bulked out with mecenaries and peasant rabble).
and I know for instance that the Battle of Troy (Greek) was waged between 'Heroes' from either side rather than full scale armies (which eventually led to the whole Horse debarcle
),
The idea of a general coordinating large scale battles is infact an anomaly - the Romans (probably) achieved it, Genghis Khan was highly organised but few others until modernish (1800s) times.
Genghis Khan divided his squads into groups of 10 who were all responsible for the success of their squad (failure of any member meant execution of the whole squad - a great incentive to cooperation) Squads were then formed into platoons of 10 squads (ie 100 men) which were formed into companies of 10 platoons (ie 1000 men)
