MY B&D 7 1/4" makes me feel much the same!
I bought the SIP 18v jobby with two batteries. Great for cuting MDF etc when boxing in pipes and the like. Mine runs out of puff pretty quickly as well, but with two batts & a 1 hour charger I can live with it. I did buy a thin kerf blade which gives a smoother cut & improves battery life.
A sparky mate swears by the Wickes 18v one.