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Lazzarae said..slammin said..I don't think the drill is fast enough.
So you need 90 degree attachment so. .. Think outside the box s bit further..... Angle grinder.

I don't think a battery angle grinder would have enough torque.
I have a good Hitachi 5" - it has the speed but definitely not the torque. Maybe a bigger one might do it!!
The tool recommended on the WinchBit website
www.winchbit.com/ is a 28v Milwaukee M28 28-Volt Lithium-Ion 1/2 in. Cordless Right Angle Drill but it doesn't appear to be available in Australia. It also looks very heavy and cumbersome as Donk has illustrated.
To my mind the perfect tool is going to be slender, lightweight, have good torque, reversible to take advantage of a two-speed winch and does not need a chuck (assuming you can weld the end of a winch handle to a piece of 1/4" hex rod).
From the locally available options, these two look OK having over 40 Nm of torque:
Makita BTL061Z 18V LXT Lithium-Ion Angle Impact Driver - 60 Nm - about $300 (skin only)
Milwaukee M18BRAID-0 18V Lithium-Ion Right Angle Impact Driver - 41 or 81 Nm of torque - about $250 (skin only)