Battery prices and technology seem to have stabilized over the last several years. There have been hints of potential breakthroughs, and I thought that Tesla's $400 million battery facility would be promising with trickle down to e-bikes, but nothing yet. For now, I complete most off road rides (15 or so miles, 2,500' ascending) with a Luna "mini", 3.5 pounds, 52V, 6 ah which is adequate for me.