I got into Milwaukee battery operated soon after they started with the LiOn batteries. The first one that I bought, probably about 2010 or earlier, was a Milwaukee M4 4-Volt Lithium-Ion 1/4 in. Cordless Hex Screwdriver w/ 1 battery and charger. They were on sale for $20@, I bought 5, one for each of my children and me.
Should have bought 20. The one I kept still works. Milwaukee still sells them.
But I'm an addict of DeWalt 20V, 20V max, FlexVolt, and the older 18V (I've an adapter for 20V/Flexvolt tools and have about 4K invested in them). Been using them for about 12 years or so. Was pleased when they came out with the FlexVolt line and the batteries are compatible with virtually all my 20V line.
When HF came out with their Lynxx 40V I bought some of their tools, pole saw, chainsaw and a couple of batteries.
Really liked both. Both worked well. Then they discontinued the line.
Will HF do the same with Bauer? with Hercules? with Atlas?
/edit - my Milwaukee M4, that I paid $20 for is now going for about $180.