If you want a battery that will last, buy the longest warranty you can find. Period. It's the only thing that matters, all of the other stuff is just marketing. All of the builders get their batteries from the same place in China, it's everything else that sets us apart.
If you want quality new cells, you are going to have to pay for them. They are very expensive to import with the trade war on-going.
Note the nomenclature difference; the only Insight pack Greentec sells with new cells is the "8Ah" for $1795.
If you really want to DIY, we still offer DIY kits of the same matched and balanced sticks that we use to assemble our completed batteries - but it costs me(and everyone else) more than $50/stick just to get them into the United States.