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Modern batteries have higher capacities and lower internal resistances than early versions. [ citation needed ] Before the mid-1950s, in the days of vacuum tube (valve) radios used batteries designed specifically for vacuum tubes, there was a nine-volt grid bias battery or (US) "C" battery , which had taps for various voltages from 1.5 to 9 volts.
The current through an ideal voltage source is completely determined by the external circuit. When connected to an open circuit, there is zero current and thus zero power. When connected to a load resistance, the current through the source approaches infinity as the load resistance approaches zero (a short circuit). Thus, an ideal voltage ...
The compliance voltage is the maximum voltage that the current source can supply to a load. Over a given load range, it is possible for some types of real current sources to exhibit nearly infinite internal resistance. However, when the current source reaches its compliance voltage, it abruptly stops being a current source.
When the power source delivers current, the measured voltage output is lower than the no-load voltage; the difference is the voltage drop (the product of current and resistance) caused by the internal resistance. The concept of internal resistance applies to all kinds of electrical sources and is useful for analyzing many types of circuits.
The current–voltage characteristics of four devices: a resistor with large resistance, a resistor with small resistance, a P–N junction diode, and a battery with nonzero internal resistance. The horizontal axis represents the voltage drop , the vertical axis the current .
The charge rate is measured based on the percentage of the amp-hour capacity the battery is fed as a steady current over the duration of the charge. Regardless of the charge speed, more energy must be supplied to the battery than its actual capacity, to account for energy loss during charging, with faster charges being more efficient.
All these lithium cells are rated nominally 3 volts (on-load), with open-circuit voltage about 3.6 volts. Manufacturers may have their own part numbers for IEC standard size cells. The capacity listed is for a constant resistance discharge down to 2.0 volts per cell. [143]
The amount of electrical current an alkaline battery can deliver is roughly proportional to its physical size. This is a result of decreasing internal resistance as the internal surface area of the cell increases. A rule of thumb is that an AA alkaline battery can deliver 700 mA without any significant heating. Larger cells, such as C and D ...