A simple mod that improves vanilla battle experience.

Feature list of version e1.8.0.3 (updated for e1.8.0.4 and e1.8.1.0, e1.9.0.0, v1.1.0.0, v1.1.0.1, v1.0.3.2) :

(v1.2.0.2)
    Accurate auto-battle-resolve (send troops / leave to others) calculation.
    Armours, equipments and associated skill level, mount and horse harness, all take into account.
    This should affect all auto-battles on the campaign map (between AIs).
(v1.2.0.1 / v1.1.5.0)
    Mount charge damage now applies to mounts without rider, fleeing mounts.
    Blunt damage to unarmored and chainmails are greatly increased, now reasonable.
    Mount charge damage is weakened. Cut damage is enhanced. Missile's relative speed bonus is enhanced.
(before v1.2.0.1 / v1.1.5.0)
(1) armor effect is enhanced and get very realistic
    1) the mathematical functions used to compute inflicted damage of blows are well designed
        -) armor would block weak blow almost completely
        -) mighty blow with huge magnitude would easily tear down armors like they were papers
        -) in the same time it will honor armor values and materials, better armor requires larger magnitude to penetrate
        -) the function designed as continuous and differentiable to provide smooth transitions
    2) armor material effect was introduced
        -) different material provide different protection against different damage types (Cut, Pierce, Blunt)
        -) chainmails are weak against blunt damage, while they provide good protection against sharp damage such as cut and pierce
            a good chainmail may completely block the sharp damage part of the strike while still be penetrated by the blunt part
            (you may wonder why chainmail is good at defending pierce damage, well, pierce strikes contain 50% blunt damage and 50% pierce damage,
              so pierce strike is different than pierce damage, I consider pierce damage as only a bonus caused by blade sharpness)
        -) plates are good to defend all types of damage, including blunt, obviously
        -) shield (which did not provide material info) s' material was considered to be leather
    3) weapon types associated with variant blunt damage percentages, based on attack types (Cut, Pierce, Blunt)
        -) all weapons inflict blunt damage, swords, spears, arrows, whatever, the difference is their blunt damage factor
        -) in general, cut strike consists of 30% blunt damage and 70% cut damage, there are exceptions such as axes' cut deal 50% blunt so they are better against armours
        -) in general, pierce strike consists of 50% blunt damage and 50% pierce damage
        -) light projectiles consist of 15% blunt damage and 85% cut or pierce damage (depending on blade type)
            lesser blunt percentage means they are more easily to be blocked by armors such as chainmail
            (e1.8.0.4) projectiles' blunt percentage is increased to 30%, providing missile weapons more effectiveness against armors
        -) blunt strikes such as those inflicted by a mace, will cause 100% blunt damage. while there are exceptions that some maces inflict pierce damage also.
    4) (e1.8.1.0) penetrated cutting damage is increased 60%, in combination, damage absorb exponent is increased 20% against cutting damage, making cutting harder to penetrate armors.
    5) (v1.1.0.0) Missiles enhanced: high-speed projectiles get an extra blow-magnitude bonus and become deadly. This bonus is insignificant under low relative speed.
        The bonus is actually a multiplier 'sqrt(x * 0.01 + 1)' to missiles' blow-magnitude, where 'x' is relative missile speed.
    6) (v1.0.3.2) pierce damage's damage absorb exponent was increased by 20% and the overall damage absorb factor was increased by 10%.
(2) swing strike is adjusted in company with armour changes
    1) magnitude bonus from weapon inertia is reduced, which means weapons with high moment of inertia are weakened
    2) damage bonus from blade sharpness is reduced, a logarithm was applied to Vanilla blade damage multipliers to weaken those OP values
(3) (e1.8.0.4) thrust strike is enhanced
    1) close thrust won't be intercepted
    2) magnitude of low collision relative speed is properly increased, while at high speed still same as Vanilla
    3) this change is balanced so that spearman are now very effective against cavalry and the strength of spear in history recurs
(4) mount charge effect is enhanced
    1) charge damage is increased (beware, charge damage is abnormal in Vanilla Custom Battle)
    2) charge damage would inflict to hostile mount as well
    3) mount charge always knock-down infantry (e1.8.0.4) that is not true anymore, now mount charge knock-down chance is based on magnitude calculation as well
    4) (e1.9.0.0) charge damage is rebalanced, mount vs mount charge gives reasonable damage
    5) (v1.1.0.1) charge magnitude was increased by 50%
(5) knock-back chance is adjusted
    1) now knock-back chance is based on blow magnitude rather than inflicted damage
    2) required attack magnitude to shrug-off, knock-back, knock-down, knock-off-mount were adjusted, and will be futher adjusted in e1.8.0.4
    3) (e1.8.0.4) athletic skill resists knock-down, riding skill resists knock-dismount
(6) missile weapons' ammunition is doubled (v1.0.3.2) this feature was removed in v1.0.3.2
(7) (e1.8.0.4) magnetic shield is disabled. that means, shield's missile hitbox size is equal to their visual size
(8) (v1.1.0.1) fix the abnormally high price of spears and ammo (this was caused by enhancement of thrust and ammo stack amount), now spears are both cheap and powerful, also, prices of bows/crossbows with high missile speed are increased (to balance missile enhancement in the previous version, these weapons are very powerful in player's hands) (v1.0.3.2) price changes of bow/crossbow/ammo were removed

The feature list aforementioned is meant to be exhausted, any features not mentioned here should be considered as bug.
There are a lot of features exist in legacy Drastic Battle (version number prefixed with "v"), but removed in present Drastic Battle (version number prefixed with "e").
Here is a incomplete list of lost old features, some of them are planned to be added back in future versions of Drastic Battle.
1) bleeding effect (it had led to conflicts with other mods, causing CTD in many computers as bug reported) (planned to return)
    sharp damage deal long period continuous bleed damage
2) crush through by blow magnitude, overwhelm parry and block by mighty strike from arbitrary direction (this feature may negatively impact early game experience, since the player rely on parrys to defeat high level enemies in arenas or battlefields, so it was removd)
3) AI parameters changes (removed since it cause negative impact on player's game experience, sometimes AI need to be a little dumb)
4) disabling mount rear-up. (was re-enabled in e1.8.0.2 as a weakening to AI cavalry)
5) mount charge self-inflicted damage (was removed since e1.7.0.0, since cavalries frequently lose their horses)
6) friendly fire, both man-made and mount-charge (was removed since e1.7.0.0 due to bad game experience) (planned to return)
7) athletic speed bonus and encumbrance speed penalty, to encourage players choosing light armours in late game (planned to return)

The following description is for legacy Drastic Battle, last version of which is v3.2.0.
Config menu was removed since e1.7.0.0.

How to open config menu:
Ctrl+Shift+D
(1) in battlefield, open battle config pages
(2) in campaign map, open campaign settings
(3) in main menu, open xml settings (since v3.0.0)
READ DESCRIPTION THERE

Features (Outdated since v2.4.0)
1. Overhauled damage calculating model which emphasizes armor effectiveness. Now high value armors should be hard to penetrate but not unbreakable. Even blunt damage can be blocked. Much effort was spent to ensure the game balance retained. (Didn't change any equipment values, only modified on formulas, so it shall be compatible with those mods that modifies "ModuleData" xml files.)
2. Realistic mount charge damage. Horse charge now inflict much more damage depend on relative speed, weight and charge property, and horses receive self-inflicted damage in the collision. Horses with low charge property will be at disadvantage in cavalry confrontation.
3. Friendly fire enabled for all circumstances. Now using short weapons in melee combat make sense, for the good of reducing friendly damage. Don't worry, your soldiers won't kill each other, any casualty caused by friendly fire will be judged as injured rather than dead.
4. Configurable and improved crush through. Ever wondered why anyone can block your great twohanded weapon with a dagger with a single hand? Now kinds of weapon's blocking capabilities are adjusted, you'll need a shield to protect yourself against those heavy attack.
5. Fixed body part armor. Now shoulder armor no longer provide armor value to chest / abdomen / arm in the damage computing process. Visual armor values are not changed.
6. No more horse rear up. Ever get annoyed when a peasant with a pitchfork stopped your fully armed warhorse in your full speed charge?
7. No more magnetic shield. The word "magnetic shield" means that shield's collision volume against missile is much bigger than its visual volume.
8. Configurable athletic skill speed bonus and encumbrance speed penalty.
9. Bleeding and spontaneous healing mechanisms based on exponential decay rate.
10... (new features in v2.4.0)

The mod is saved game compatible.
The mod is clean. It doesn't leave any data into your saved games / game files folder.
Always guarantee that all functions of the module can be turned off / configured.
Press Ctrl+Shift+D in battlefield or in campaign map to open two different config menu.
All configuration files are located in Modules/DrasticBattle.

Compared to the similar battle overhaul mod Realistic Battle, Drastic Battle follows a more conservative design philosophy that it didn't modify on any equipment properties and its functionalities are totally invisible outside the config menu. The aim is to achieve greater compatiblities while it brings a lot of improvements to game battle experience.
Compatible with Realistic Battle AI Module.
Conflict with Realistic Battle Combat Module.



About Armor Penetration and Material Parameters (Outdated: formulas changed in v2.4.0)
The armor effectiveness related parameters are probably the most confusing parameters among so many parameters in config menu.
Although those parameters are already well adjusted as properly balanced in current version you may still want to tweak them slightly to fit to your interest.

Vanilla Damage Calculate Process
Formula:
d(r, m) = max{0, 100/(100+ar)*m-tr}
d, damage
r, armor value
m, blow magnitude
a, armor absorb main factor
t, armor threshold of that type of damage
The damage calculate procedure could be seperated into two stage, the absorption stage and threshold stage.
First, absorption stage, decides how much of the fraction of magnitude remain after absorption apllied. In vanilla case, the fraction is '100/(100+ar)', it's a number between 0 and 1, it multiplies the magnitude then pass the result to threshold stage. As you can see, the fraction amount depends on armor value only, since 'a' is a constant.
Second, threshold stage, subtract the magnitude remain with 'tr'. For blunt damage, there is no threshold stage.

Armor Penetration Mechanism
The penetration mechanism introduced in Drastic Battle v2.1.0 aims to improve vanilla absorption process in such aspect that absorption fraction, which only depends on armor value in vanilla, should also be related to the blow magnitude. Blunt damage should be not the only way to crack down heavy armor. Cut damage, with adequate blow magnitude, can break the armor too. The idea is, the higher the blow magnitude, the higher the magnitude percentages remain after the absorption stage.
Formula:
d(r, m) = max{0, s*m-tr}
s(r, m) = 100/(100+(100+m/p)/(100+mp)*ar)
s, absorption remain fraction
p, armor penetration factor
By design, the armor penetration factor should cause the effect intended when it's greater than 1. Interestingly, when it's located in (0,1), it will have the opposite effect i.e. higher the blow magnitude, higher the magnitude percentages absorbed, in which case the overall armor effectiveness are drastically improved.
And of course, when armor penetration factor is 1, it doesn't effect, providing vanilla absorption percentages that unrelated with magnitude.
Here is an example of absorption remain fraction, when penetration factor is 1.8, material effect is 1 (off), compared to penetration factor 1 (off), material effect 1 (off).
In which x-axis represents armor value, y-axis represents blow magnitude, z-axis represents absorption remain fraction.
Here is another example, which makes use of material effect.

Material Effect Parameters
There is only four type of armor material in current bannerlord edition, and they are discrete, unfortunately, no mixed state like 75% chainmail and 25% plate.
In versions before v2.3, material parameters are used as multipliers on armor thresholds affect in threshold stage. The effect was not ideal, since blunt threshold is much less than other thresholds, the material parameters' effect is unfair to different type of damage and almost useless to blunt damage.
Due to many drawbacks, material parameters are redesigned and given great significance in v2.3.0. They work in absorption stage and serve as exponent of 's', the absorption remain fraction.
Formula:
d(r, m) = max{0, s^e*m-tr}
e, material effect parameter