Battleragers are a major pain as a mage, especially somebody new to the game. The best solution is being able to kill them, but until you reach that point, you have to be able to escape.

The first thing you have to do is see them coming. Any time you're in an area where you're likely to be attacked (like ranking), you need to type "where" constantly.

Basically, every other command should be "where":

c magicmissile
where
c magicmissile
where
lash
where

This seems excessive, but then you will always see when a potential enemy is approaching. That means you'll be able to get away. If you are surpised by somebody bashing you, you're going to die.

Second part of this is to carry teleport and word of recall potions, especially if you don't have the spells yet. Set them up on an alias so you won't fumble around trying to type it out in an emergency. Some cities sell them much cheaper than others. Shop around for a good bargain so you can always be stocked.