Battle enchantments are spells like Light of the Northern Star and Storm that create an ongoing effect that affects the entire battlefield until the caster leaves the battlefield by any means. Typically this occurs through death or retreat, but can more rarely happen through returning or becoming banished to another plane.

These generally require gems, a lot of fatigue, and high paths, but can be extremely powerful. Some battlefield enchantments do continual damage to all units of a particular type; these are particularly powerful if your army is resistant or immune but the enemy's army is not. Examples of these include Rigor Mortis, Foul Vapors, Fire Storm, and Wrathful Skies.

Battle Enchantment	Paths	Gems	Research	Effect
Light of the Northern Star	3	2	Conjuration 4	+1 Astral to all astral mages on the battlefield.
Howl	3	3	Conjuration 5	Every 320 ticks, wolves appear at the edge of the battlefield. 1d3 are summoned if the provinces is neither a forest nor a mountain. 1d6 are instead summoned in forests and mountains. The wolf die rolls can explode.
Shark Attack	3	3	Conjuration 6	Sharks appear at the edge of the battlefield when wounded. They mostly, but not always, attack enemies.
Solar Eclipse	31	1	Alteration 5	The battlefield becomes dark, applying darkness penalties of -3 to attack, defence, and precision.
Darkness	4	4	Alteration 6	The battlefield becomes dark, applying darkness penalties of -6 to attack, defence, and precision.
Rain	2	1	Evocation 2	It starts to rain on the battlefield. Heat aura effect is reduced, Fire magic fatigue is doubled. Creatures on fire are very likely to stop burning quickly. If cast in cold it snows instead, which does not double fire magic fatigue.
Mist	3	1	Evocation 3	Base precision is halved, rounding down.
Storm	4	1	Evocation 4	Flight is prevented for all creatures without storm immunity. 50% of missiles are lost. All creatures without storm immunity have their precision halved. Also applies Rain.
Wrathful Skies	5	2	Evocation 6	Strikes 0.3% of the battlefield with 15 AN shock damage every 320 ticks. Storm doubles the area struck. Expected hits per tile per round: 7%
Wailing Winds	41	2	Evocation 6	Strikes 5% of the battlefield with a strength 1 Fear effect every 320 ticks. Does not affect friendlies.
Rain of Stones	31	1	Evocation 7	Every 320 ticks, strikes 1% of the battlefield with falling stones that inflict 5 nonmagical blunt damage to a creature in the affected square. Appears to be more likely to hit heads. Expected hits per tile per round: 23%
Fire Storm	5	3	Evocation 7	Strikes 3% of the battlefield with 6 AP fire damage every 320 ticks. Expected hits per tile per round: 70%
Acid Storm	41	3	Evocation 7	Strikes 3% of the battlefield with 4 AP acid damage every 320 ticks. Expected hits per tile per round: 7%0
Astral Tempest	5	2	Evocation 8	Every 320 ticks: Strikes 2% of the battlefield with 1 AN magic damage, negated by MR. Additionally strikes 4% of the battlefield with 100 Interrupt damage, that does not affect Mindless creatures and can be negated by passing a MR check. Expected hits per tile per round for damage: 7% Expected hits per tile per round for interupt: 14%
Meteor Shower	54	3	Evocation 9	Every 320 ticks, makes five rolls each with a 15% chance of success. Each success drops a meteor randomly on the battlefield which inflicts 150 magical blunt damage. Expected hits per tile per round: 0.55% 1)
Quagmire	4	1	Enchantment 5	Creatures without swamp survival have -1 attack, -1 defence, +2 encumbrance, and -20% combat speed.
Friendly Currents	3	1	Enchantment 5
Foul Vapors	31	1	Enchantment 5	Strikes 1% of the battlefield with 5 AN poison damage every 320 ticks. Expected hits per tile per round: 23%
Rigor Mortis	4	3	Enchantment 6	Strikes 3% of the battlefield with 10 AN fatigue damage every 320 ticks. Undead and inanimates are unaffected.
Relief	5	1	Enchantment 6	Strikes 6% of the field every 320 ticks. Friendly units lose 1 fatigue.
Heat from Hell	4	2	Enchantment 6	Strikes 3% of the battlefield with AN fire fatigue damage every 320 ticks. The amount of damage dealt is 5+Heat scale, -3 if raining. Does nothing if Grip of Winter is also active.
Grip of Winter	4	2	Enchantment 6	Strikes 3% of the battlefield with AN cold fatigue damage every 320 ticks. The amount of damage dealt is 4+Cold scale, +2 if it is snowing and a storm is present. Does nothing if Heat from Hell is also active.
Solar Brilliance	5	3	Enchantment 7	Every 320 ticks: 5% of the battlefield must make an easy MR check or become blinded. 5% of the battlefield is struck for 5 AP damage if Undead or Demonic, with an easy MR check to negate. Expected hits per tile per round: 117%
Mists of Deception	6	2	Enchantment 8	Applies Mist. Summons 1 phantasm per turn for each air level of the caster.
Fields of the Dead	52	1	Enchantment 9
Demon Cleansing	5	1	Enchantment 9	All demons on the battlefield take double damage.
The Ravenous Swarm	3	1	Thaumaturgy 5	A random undead target takes 7 AN damage per round. If there are no undead, it begins attacking the living instead.
Growing Fury	4	1	Thaumaturgy 5	Affects the battlefield every 320 ticks. All friendly units with an inherent berserker value, or those whose current hitpoints are lower than their maximum immediately go berserk. Other friendly units have a flat 5% chance instead. As with usual berserking, this does not affect most mounted units, Mindless units, or Slave Vessels.
Soul Drain	55	5	Thaumaturgy 8	3% of the battlefield suffers 2 AN magical life steal every 320 ticks. Magic resistance avoids the damage. Expected hits per tile per round: 70%
Blood Rain	3	3	Blood 7	All units on the battlefield suffer -4 morale.
Divine Channeling	5			All friendly 1 priests gain +1 holy level.
Dance of the Morrigans (EA Fomoria)	52	4	Conjuration 8
The Ark	Caused by the presence of the The Ark artifact in battle.			Strikes 3% of the battlefield every 320 ticks. All units affected make a MR check. Sacred units, prophets, or pretenders belonging to Ark's owner are entirely unaffected, even upon failing this. All other units are struck for 2 AN magical damage. Additionally, there are 20% chances, rolled independently of each other, that each struck unit becomes diseased and blinded2).

Whilst not technically battle enchantments, the presence of the following Global Enchantments act as if they were battle enchantments:

Global Enchantment	Paths	Gems	Research	Effect
The Eyes of God	5	50	Enchantment 5	Active only in its caster's dominion. Every 320 ticks, all enemy illusionary creatures must make a MR check or take 999 AN magical damage.
Foul Air	51	75	Thaumaturgy 6	Active only in land provinces. Every 320 ticks, applies disease to any unit in battle whose current hitpoints are less than their maximum, and that are not Demonic or Inanimate.