Like my brother always told me - "if it aint broke, don't fix it."
Lead batteries work well, the lead it cheap and it's easily recycled.
OTOH, Honda and Toyota are using Nickle metal hydride batteries in their hybrid vehicles.

On the thin CD like battery, it's already been done... it's even flexible.

http://www.solicore.com/11-09-03-a.html
http://www.solicore.com/tech.html
http://web-japan.org/trends/science/sci060119.html