Well, to some of what you say, I disagree. Lead is just fine for a conversion of a motorcycle. The first itteration of my motorcycle was using 12 Power Patrol SLA1116 18Ah 12V batteries I got free. They got me ~15 miles. It was a great way to launch the project for a fairly cheap price. Yes, he could go lithium directly, but if he can source cheap lead, there's nothing wrong with it. Most people that do motorcycle conversions have used Lead for their first bike and then work out all the kinks and move to lithium. I know lots of people use larger SLA batteries and get 30 or so miles out of them.
Now, as far as range and weight, I agree....The Lead pack was roughly 170lbs in my first version (480lbs for the whole bike, near stock weight). The lithium in my new version should weigh about 105lbs for 160 cells of the headway 38120S batteries (~70lbs lighter than stock weight).
I'm still in the tail end of my "upgrade" froml lead/brushed motor to lithium/AC Induction, but I know that I can fit more than double the capacity in the same space, and less weight.