I am now ahead with the knowledge of battery technology. NiFe batteries are high-tech and not simple to build in a mass. Only when you accept a short life time and low performance - you can make it simple. We have now developed a new battery that is competitive. The manufacturing and R&D efforts are gigantic. If we can sell now in a mass, we want to lower the cost by economy of scale. I put all in a working sheet: http://crystal-green-energy.simplesite.com
Not small scale, so not OSE spec, but maybe we can learn something.