Battery Issues

[teenix]

Maybe both battery packs, being of the same age, have partially failed and are causing the problems. Both calculators appear to have a CPU board issue which may be caused by the batteries. The bright red dot indicates very low battery voltage which may be too low to operate the calculator properly. Have you tried a new battery? Are the CPU boards clean and free of corrosion?

As I understand NiCads, (if that is what they are) they should have fairly constant voltage until discharged, (3 x 1.2V = 3.6V). 4.26V seems very odd then.

If the battery is damaged, the charger/battery combination, could also cause a problem, which may risk damage to the calculator. You could load the battery out of the calculator with a 27 ohm 1 watt resistor (about 130mA) and measure the voltage. If it is charged, it should be close to nominal 3.6V if that is what they are specified to be. The resistor will heat up a bit.

I think the 35 can handle 3xAA cells (4.5V), but not sure with the 67. This voltage feeds the card reader chip directly but I don't know if the chip is spec'd to handle the higher voltage directly. The HP-97 uses the same chip with a higher 5V battery voltage but has extra circuitry which may limit current/voltage for the motor.

cheers

Tony