1.5V AA Alkaline Battery
The standard cylindrical single-cell battery for low-to-moderate drain devices, delivering a nominal 1.5V that sags noticeably under load rather than holding a flat regulated voltage.
How this component works
A battery converts stored chemical energy into electrical energy, providing the electromotive force (voltage) that drives current through a circuit. Inside the battery, a chemical reaction between an anode, a cathode, and an electrolyte produces a steady DC voltage.
In circuit diagrams, batteries are often modeled as ideal voltage sources. However, real batteries have internal resistance, which causes their terminal voltage to drop when supplying heavy currents. The larger the current draw, the more pronounced this voltage sag becomes.
Connecting batteries in series increases the total voltage (e.g., two 1.5V AA batteries yield 3.0V), while connecting them in parallel increases the total current capacity (Ah or mAh) without changing the voltage.
Deep Dive: AA Battery (1.5V)
The 1.5V printed on an AA cell is a nominal open-circuit figure, not a guaranteed operating voltage. Under load, the cell's internal resistance (roughly 0.15-0.3Ω when fresh, rising as the cell depletes) causes a real, measurable voltage drop: pull 100mA and Ohm's law alone (V = IR) predicts a 15-30mV sag from internal resistance, but the bigger effect is the cell's own discharge curve — alkaline chemistry doesn't hold a flat plateau like a lithium cell does, so terminal voltage declines gradually and continuously from about 1.6V fresh down toward 0.9-1.0V as the cell is considered 'dead' by most devices.
This is why series-stacking AA cells is the default hobbyist technique for reaching standard rails: two cells nominally give 3V (a common logic-level supply for 3.3V-tolerant circuits with a small drop margin), four give 6V (a classic small-motor or relay-coil voltage), and six give 9V — deliberately overlapping with the PP3 9V battery's voltage but built from cheaper, higher-capacity cells. The tradeoff for using AA over a single-cell design is physical size and cell count, not price-per-mAh, where AA alkaline is usually the cheaper option.
Common Use Cases
- Powering TV remotes, wall clocks, and other low continuous-drain devices where shelf life matters more than peak current
- Stacked in series (2x for 3V, 4x for 6V) as the classic breadboard power source for simple logic or LED circuits
- Driving small hobby motors or LED circuits where a disposable, no-charger-needed supply is preferred over rechargeables
Frequently Asked Questions
Why does my circuit read less than 1.5V from a fresh AA battery?
Alkaline cells sag under load rather than holding a flat voltage. A fresh AA reads close to 1.6V open-circuit, but under a 100mA draw through its ~0.2Ω internal resistance it can measure closer to 1.4-1.5V, and that number keeps dropping as the cell depletes — unlike a regulated supply, there is no flat plateau.
Why do circuits stack multiple AA batteries instead of using one higher-voltage cell?
AA is a fixed 1.5V chemistry, so reaching common logic rails like 3V, 4.5V, or 6V means putting cells in series. It also lets a project use whatever battery holder size fits, rather than sourcing a nonstandard single high-voltage cell.
Can a single AA battery reliably drive a small DC motor?
It can start one, but poorly — alkaline's rising internal resistance under sustained high current causes the voltage to sag hard during motor stall or startup current spikes, which is why multi-cell packs or rechargeable NiMH (which holds voltage better under load despite a lower 1.2V nominal) are preferred for motor-driven projects.