I think most "proper" impact wrenches stayed with NiCads due to high current requirements for ages. The early Lithium ones were, and mostly still are, less able to deal with this application.
NiCads need a lot more love and care, as don't respond well to being left flat, or cold temps (like a garage over the winter). Though have the bonus of easily supplying high current, and not busting into flames at 67C when charging/discharging.
Be aware of naming, and Impact Driver is a screwdriver, not anything you can use on a car.
My DeWalt impact wrench is claimed to be about 190Nm from memory, with a variable trigger (REALLY useful) and a small body (more versatile).
The Clarke (identical to Sealey and every other rebrand buying the same Chinese tat) claims 450Nm, on/off trigger, and large body. Its shite. Utter shite. Need to loosen wheelbolts first, its big, heavy and cumbersome, easy to crossthread due to non variable trigger, and heading for the skip if little bro doesn't want it.