Re: Lithium over Lead? It's really not that clear.
Only a couple states offer free HOV lane access for electric cars. In Minnesota there is no HOV sticker, you pay 25 or 50 cents(or more if that lane starts getting congested to a speed lower than 50mph) to access the lane if you aren't carpooling on the highways that charge the express lane toll for that lane if you aren't a carpooling vehicle, motorcycle, or bus. I've never been on those highways where it is busy enough to even think about buying the electronic unit though. IMHO, I've never really understood the point, it ends up becoming a political issue for people to attack hybrid and electric cars.
There are ROI points that don't include the batteries too though, the other components can be used in a different car. The battery could be too, if someone decided to swap cars, as long as everything is compatible.
I think its clear to go with lithium, it's about the only real way to get a higher performance system that is lightweight, much easier to fit with more cargo room, longer life, they don't need to be watered like a plant to prevent them from dying, you can go higher voltage without having the excess weight without the extra capacity like lead, peukert requires you to buy more capacity to cover for it, same with adding extra capacity(and weight) to cover the range you lose when the lead-acid pack starts to dig itself a hole, lower efficiency charging and discharging. These are a few of the extra costs that aren't as apparent when going with lead.