Seconding that advice to just use prismatic lifepo cells. Those have become really cheap, too: You can order brandnew 1kWh cells for $60ish + shipping even if you only need single digit quantities (those want to be squished a bit for longevity, so you might have to design a suitable enclosure).

Energy autarky has never been so affordable, progress on batteries and solar panels was awesome over the last decade.