A buddy of mine has Ridgid tools and has got a few batteries swapped out. For him it was a smooth process, and tried pushing me to buy them though I went with Milwaukee. I don't see the battery lifetime warranty as a plus as by the time most of my batteries start to die, their ecosystem and batteries will have changed and I would have had to buy all new tools anyways.
My dad has had Ryobi 18V stuff for about 10 years now. NiCd batteries from 10 years ago are long gone, but the lithium ones have held up well. We've built more sheds, garages, decks, walls, and done more home renos than you can shake a stick at with them. Really good tools for the price, and one of the most diverse tool line-ups out there.
I have Milwaukee M12 stuff. Really like them for their more automotive oriented tool line-up and lightweight. Depends on what you're doing with them, I'd say stick with 18 or 20V. Biggest issue with the M12 drills and drivers is that they are super easy to stall out. You'd never drive a 2.5" wood screw into a 2x4, or drill a hole through one to run a wire through it, they just don't have the power. I'm going to grab some M18 FUEL stuff next time its on sale, but if you don't use them much they are just way to much money.
I hate corded tools with a passion. Anything without an electric brake is useless to me, and it's very uncommon to get a corded tool with a brake.