electric bike highty efficient and latest battery.??????

I have a crystalite 408/412 rear hub on my mountain bike. It takes four 12 volt Sealed Lead Acid batteries that were very heavy and made the bike ride wierd. I was looking for battery suggestions that will not be as heavy. Also I would be nice if they did not cost an arm and a leg. Thanks.

hi all i love riding to work on electric.
scooter. but i really need to get fit but .not ready to give up electric..!!
so why not combine the two electric bike !! i carn't afford the electric pedal motorbike it's german forgotten .
the name but its sumthing like £10.000/ £20.000 wow .
thats steap ..
well what i am after is a super efficient motor / latest technology battery super light and compact .
and needs to be a mtb ? but needs to look very moden / light. have at least 5 gears. and needs to be ( very modern )!! looking.