8 * 1.2V (assuming NiCd/NiMH voltage) is 9.6 V; that, one silicon (i.e. normal rectifier) diode, and a ~9 Ohm resistor of appropriate power rating should yield a workable power supply, which will fall inside the Nokia specifications (for I-V characteristic at least). 8 * 1.5V, OTOH, is 12 V; the maximum voltage permitted is 9.3V, so this would be outside the charger spec and potentially harmful to the device.