You absolutely want to make this with a number of small passes! While your little battery powered router is a great tool (and on my shopping list), it is not a production quality tool designed to route out a 1/2 x 3/4" rabbet in one pass.
I would strongly recommend using Criggie's suggestions for temporarily making a wider base for your router to sit on while you're doing this, both for the accuracy of your cut and for the safety of your fingers.
I would suggest a small straight cutting bit that can reach down the 1/2" depth of your cut. Make your first pass at about 1/8" depth, and rout out the entire area, then reset the bit to 1/4" deep and make another pass. Continue making passes about 1/8" deeper each time until you've reached your final depth. Doing this will yield a flat bottom rabbet with a fairly sharp 90° corner at the bottom - you will have rounded vertical "corners", and can clean these up with a sharp chisel (also recommended by Criggie) if you need them to be nice and square.
If this cabinet is not yet attached to anything, you might consider tipping it on its side (lay it on a piece of cardboard if the other side is finished and to be exposed) and getting a bit that will cut to a depth of 3/4". You can use the wide flat side of the cabinet (currently vertical, along the plane of the 1/2" dimension) as a much more stable base for the router, and probably won't have to add on any scrap to provide an additional platform. You'll need to make more passes (I'd still recommend only 1/8" deep at a time) to get to the final 3/4" depth, but you'll get there in the end.
Attempting to hog this all out in one single pass will be very hard on your small router, will likely end up in a lot of burning of the wood, will not give you a very nice cut, and could cause the thin 1/4" shaft of your router to snap, hurling a small, hot, very sharp projectile at high speed in a random direction across your room. Most people consider that a
Bad Thing™. Making that cut in one pass really is only in the purview of heavy duty, industrial strength, production shop level of shaping machines that are set up to make 1000s of cuts like this each shift.
Finally, if you have more woodworking type questions, I'd encourage you to check out Woodworking.SE (oddly, dedicated to woodworking! ;)