The only way to make lead based battery to be more efficient is to build it in some nano technology way , which wouldn't be cheaper (on the contrary). Lead has large mass and you can't reduce that mass and keep the energy storage capacity (it has some connection with reacting surfaces of electrodes in the cell). Now , what can be done, is to improve the life (shelf and working life) of the cells and percentage of stored energy use (ie - your battery should be safe to 80-90% DOD in many more cycles than today's SLA).
But, with carbon based (nano) technology and Lithium and all other stuff, it's not likely to happen. And there are alternative researches of "free energy" and what not, so it is more probable direction of research for handling the energy storage and use and availability .