hp classic calculator charger without battery pack

[teenix]

The Classic chargers like 35, 45, 55, 65, 70, 80, (and 67?) have a logic voltage supply available as well as a charging current circuit for the battery. The 35, 45, and 70 owners manual says it is ok to run these on the charger without a battery installed. Why the other Classics don't, I'm not sure why as they are all much the same. Even if it is ok, then what condition is the battery charge circuitry and connections. (Corrosion etc).

For other models: 65, 67 21, 22, etc, the manual says it may cause damage to the calculator circuitry, and indeed it does. Sadly, some people have been stung by this.

Also, the calculator/charger components are quite old now and may not take too kindly to power spikes by plugging in a charger that is already connected to the mains for example, as happens quite often these days with modern phones etc. This warning also appears in the manuals.

All said and done, it is always wise not to run any of these calculator models from the charger at all, battery or no battery, and also charge the batteries outside the calculator.

cheers

Tony