Ener1 is producing Lithium-ion batteries for vehicle and commercial use. They are using nano technology and are the only US Mfg that uses flat, rather than cylindrical construction. I have emailed them asking for information on batteries that could be used in a golf cart or LSV application. Their responses have been courteous but I don't think they see this industry as a potential market. If you would like to upgrade to Lithium-ion please email them:
http://enerdel.com/mos/Contact_Us/
I am going to post their contact information on every electric vehicle website. Maybe if they got enough requests, they would consider building some batteries that would be appropriate for our use.
I would love to see some 36, 48, and 72 volt battery packs that were light and compact.