Q: Recharging HP 21 calculator?



Archived from groups: comp.sys.hp.hardware (More info?)

I have a HP 21 calculator (the old one from the 70's) It's out of battery
and I want it recharged. I don't have the original charger and was going
to use another power source. It seems (from HPmuseum) that 10 Volt AC /
1.8 VA is what I need.

Questions: Is that right, should I really use AC not DC? What are + and -
in the little conector on the back?

Any help is apprisiated


Jul 10, 2009
Just chance upon this. HP just make digital versions of their calculators for use on iPhone.

If you are still using your calculator, simply removed the 2 old batteries and insert AA size dry cells or rechargeble batteries. Then you can recharge the batteries outside of the calculators.

Never leave batteries discharged in the calculator for long, as they can leak and and really damage your calculator. See battery damage of this
Hewlett Packard HP-21 calculator at this site

The battery charger termimals on the calculator is for a AC input of about 9V AC. If you dont have the original adapter suppose you can modified a standard one bought from the store.