There are many reasons to love the HP calcs, but I think the keyboard doesn't get enough praise. I have never found another calculator as satisfying to use. I heard from owners of the Swiss that it's not quite as good.
FYI the company that took over the HP Calculator business is releasing a "HP-15C Collector's Edition" that fixes the HP-15C Limited Edition's bugs, but it's a limited edition as well so if you want one you'd better preorder. It won't have the amazing battery life of the original, but it will be orders of magnitude faster, and reports say build quality is good, unlike newer HPs.
I fully expect it to outlive both of us - due to HP's excellent dual-shot key molding that embeds the key legends into the keys themselves, it looks nearly new less a few scratches and dings imposed by the real world. This may have been one of the last times a product was truly designed to last indefinitely. And yeah, I suspect self-discharge of the batteries is at least on par with the actual power usage of the calculator...