Good point, and good examples. Excited online discussion about companies like those are what I mean when I say it's popular on the internet. It's not impossib

Good point, and good examples. Excited online discussion about companies like those are what I mean when I say it's popular on the internet. It's not impossible, it's just not the technology I would be betting on. To get a sense of what one is up against, you can work through the math comparing gravitational potential energy to electrical potential in typical batteries. I can't find a good link right now, but what I remember finding is that (in the ideal) a typical lead acid car battery has enough stored energy to lift itself into space! Conversely, if you wanted to store the same amount of energy as in a typical car battery, you'd need to be dropping that amount of weight from the top of the atmosphere all the way to the ground.