Typical D cell batteries NiCad or otherwise are 1.2 volts.
The cell voltage.
NiCad batteries don't charge to a specific voltage. While you would certainly place limits on voltage and current, the primary detection of full charge is to sense the long term slope of the voltage, and to detect the knee point (change in slope) that occurs at full charge.
Battery voltage / number of cells = cell voltage 12/6 = 2 volts cell voltage
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The different chemistries makes a different voltage. The alkaline is 1.5 volts and the NiCad is 1.2 when fully charged. If it will work with the lower voltage then it may only assume that the battery is low. But when the NiCad actually gets low then the device may not work properly.
I talked to an expert at Total Battery and he said "yes, you can substitute NiMh batteries instead of NiCad, and still use the same charger." I dug up one of my old dead NiCad AA batteries and it's the same voltage as the AA NiMh battery. Ray B.
The number of cells in a battery determine the battery's voltage. Different types of batteries have different cell voltages. The cell voltage is dependant on the reactive metals used. A typical car battery will have six cells. Because a typical cell voltage has a source voltage of approximately 2.0 volts, this makes a car battery produce a voltage of 12 volts.
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A solar cell does not store electricity. It charges a battery that stores electricity. The voltage of a battery can be found by connecting a voltmeter to the battery terminals.
There is no standardized voltage for wet cell batteries, but 1.5 V is a common value.