I have and have used this exact (Stanley right?) model for the past two years or so - couldn't be more pleased. I only charged it twice but it never really got weak on me. i recharged it just to be safe. It jump started my DEAD truck battery a half a dozen times earler this summer with no problems whatsoever. Very strong unit. I also use this unit to inflate my kids bike tires and my riding mower tires. i no longer keep jumpers in my truck and this thing lays flat in the under rear seat tray.
Sam's had a 350 unit for $5 cheaper but the extra money is a no brainer for the 450.