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3ah on an 8 inch auger will be pushing it.
After over 20 pages of problems with the new Ridgid Octane I'd avoid that tool like the plague. I'm 3 years in with my 2603-22 Milwaukee Fuel and 8"K Drill setup with thousands of holes drilled with it and have had zero issues. I run the 9.0 and 12.0 batteries. I would buy the Fuel tool again.
Does the Milwaukee have a lifetime warranty? If so I would think about going that direction. With Ridgid you get the LSA and it covers, tools and batteries for life. That's hard to beat and the older I get the more I try to only buy things with lifetime warranties.
Be hey at least they have the lifetime warranty. Go thing since your going to need it.