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HP's Classic calculators changed the world. But they used rechargeable NiCd battery packs. Not only did they run down quickly, they took hours to charge, had a terrible "memory effect", and a short service life.
I will build you an adapter to instead run your HP Classic calculator from any AA batteries, including long-lasting Alkalines and fast-charging NiMHs. I've tested these on my HP 35, 45 and 65 but they should also work with the 55, 70 and 80.
Modern batteries can power my HPs for days, and when they run down I don't have to use the AC adapter or face an hours-long NiCad recharge cycle. I just pop in whatever fresh batteries I have on-hand. Worst case, I'm only 15 minutes away from a fast charge of smart NiMHs.
I used to cut the plastic parts from polystyrene, but these days I have them 3D-printed (as shown at right). It increases my costs, but it decreases the work, so I still offer them for $45.00, including US shipping. I accept payment by check, money order, or PayPal.
Email me at bobwolfson@gmail.com if you're interested.
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