I've got an HP40gs laying around from my physics days, I should really get some batteries for it. Picked up the cheapest scientific calculator I could for the g

I've got an HP40gs laying around from my physics days, I should really get some batteries for it. Picked up the cheapest scientific calculator I could for the geology degree, a Sharp EL-501w (The casio fx260 is near and dear to my heart but it doesn't have a second line/history which is very handy) and I still pick that up pretty frequently, my phone has rpncalc, which is great and all but it doesn't come to hand as easily.