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I "inherited" an HP 21 from a colleague who cannot resist collecting things that look like they could work. Being in Namibia the chances of laying my hands on a replacement battery pack and charger are slim. So I replaced the NICd cells with 2 std aa penlight batteries. The calculator works ! ! ! !

However, I am concerned that the higher voltage may cause damage. Can anybody give me advice?


You should have few to no problems. many people have done it in the past. You can get individual NiCAd or NiMH rechargable cells also.

In my experience, alkaline AA batteries are acceptable, the excess voltage is within tolerances. Of course, I cannot offer any warranty. Please never use the AC adapter with non-rechargeable batteries; only use it with proven, good rechargeables and with clean contacts. Failure to do so will damage your calculator in a split second and beyond repairability. If possible, just avoid the AC adapter, and use an external recharger.