If you've bought or own a bare tool impact driver or similar power tool, you're going to need a set of cordless drill batteries. Simply put, no drill battery equals no power. There's a variety available, from 18v batteries up to 24v - the most powerful.
Different makes appear to work slightly different - some take a lengthy recharge, others less so. Some will power up and down equally - making a double battery pack an extremely sensible option. One charging, one in use - never without power.
Of the ones available you'll find the lithium-ion, Ni-Can and Ni-Mh batteries. Which one you choose depends on your needs and every one's got an opinion. My advice is they all have their own benefits and I tend not to choose a cordless battery for what's in it so much as how it performs and feels in my hand.