John, I think that you will regret this decision when you finally see one and get a chance to see just how good they are, for me, the reduction in the weight I'm carrying up and down steeps banks and hills has been a real boon. If your pockets are deep enough you could buy two and simple swap the lamp over when the first has given out. Two of these packs would only weigh 3 1/2 lbs altogether against I would guess 10-20lbs for your current battery.
Hope they're the biz 'cos I've just ordered one. Cheers, D.