If you don't want to spend the money for LIFEPO4s now, you could build a battery pack out of NIMH or NICAD batteries with high C-ratings. (It's generally much cheaper to buy these cells than individual LIFEPO4 cells. Check out all-battery.com, they often have bulk sales.) NIMH and NICAD batteries weigh less than SLAs and have more charging cycles, if handled properly. You have to realize that no battery can survive long without proper handling. You don't want to over discharge them (even SLAs) and you must recharge frequently (as soon as you've used them with SLAs). Battery technology is the most disappointing feature of any EV system. The technology still lags behind. Yes, LIFEPO4 is safer than LiPOLY and seems better suited for EVs since even traditional LiION with Magnesium Oxide or Cobalt can catch fire or explode if mishandled, but they have issues, too. If you want a 48V SLA pack, then you should consider towing a trailer and placing them in it. Good luck.