I've seen a loss of 3% to 7% with charging and pulling from my home solar batteries. I have no doubt that temperature is a factor. I agree with you that a 20% loss of any energy storage is ridiculous. But as far as where that extra energy comes from, it comes from the excess energy on days you have more energy coming in than you consume. That's not a perfect solution. But as far as making this freedom loving American a little less dependent on things the government overregulates (like energy), it's working for me.
Even if I didn’t mind my house looking like a commercial building I don’t have enough roof with southern exposure for even one solar panel. And it’s a 2,400 SF home.