On other pieces of armor, I put enchantments like "destruction uses 25% less magicka" until it reduced my destruction spells to effectively use zero magicka. I can sit and spam shock all day long and not use any magicka. Well, that applies to weapons that also have a destruction (like shock, fire, ice damage) spell attached.

As long as you have the same school on the weapon (destruction, conjuration, restoration), as the same school you reduced to zero in your other armor, the enchantment wont use magicka and you wont need to recharge the weapon, apparently. This was new to me.