I don't think any of the Sears power tools come with a lifetime warranty like their hand tools. Glad to see you upgraded to a better impact wrench. It makes a huge difference.
I believe my 18V makita batteries are NiMH, and they did last around 5 years. Cordless is almost mandatory at the track, unless you lug a compressor around.
I don't buy Sears power tools, and prefer Ingersol Rand for air tools.