Life span of an HP Calculator

[teenix]

The 97 (and unreleased 95C) actually have an overvoltage circuit which trips if the battery on charge goes above 6V. It would also work with the battery out of circuit, however you would lose some of the AC ripple dampening effect of the battery should this be removed. The manual mentions improper displays running only on the AC charger, probably caused by the excessive ripple. The charger on its own won't power the card reader and printer properly either. The service manual also mentions AC adaptor only will not cause damage, however the manual also says the battery [must] remain in the calculator during operation.

The 91 and 92 Topcats do not have this over voltage protection. The manual says operation will be the same as the 97 (95C) without batteries.

To preserve the wellbeing of the calculator, the overall consensus is to...
Use batteries in good condition
Keep battery terminals clean - including charger port (Classics, 65, & 67)
Charge batteries externally
Do not use the AC charger, unless charging external

The power switch is also part of the battery circuit so it should receive some maintenance every now and then. Most notably, the original contact lubricant dries up and goes hard.

cheers

Tony