Batteries in Milli Volt Scale

Is there any firm that manufactures and sells retail quantities of Milli Volt batteries

Googling gave too many large scale vendors and no retailers and at the same some local shops are not having these batteries?

Is there any firm that will have such a small scale rechargeable millivolt batteries?

Otherwise do tell on how to make a rechargeable millivolt battery that would also be helpful in many ways?

Ps: Links are too hard to understand when it comes to making rechargeable batteries they are having too many chemical equations I can't understand them