The Lord of the Rings: The Battle for Middle-Earth II Hints

If you create a hero with the Self-Heal power, it can be used without recharging it. In a battle, select your hero, click Self-Heal, and then immediately right-click somewhere else, making a move order. The Self-Heal power will be used, but not start the recharge, allowing you to use this whenever you want.

This glitch has been fixed in recent updates by EA Games, but if you have an older version of the game it will work.

-First, get the power "Summon Rangers" and build a well.
-Then, use the power, and let the units take casualties, but do NOT let them die.
-Bring them back to the well and heal them. The healed units will not vanish when the elapsed time is up.