An alkaline battery can show a normal voltage while resting but drop when a device starts operating. This matters in applications such as toys, shavers, cameras, and photo flashes, which Tiger Head lists for its LR6/AA and LR03/AAA alkaline batteries. Motors and flash circuits create short periods of higher current demand. If the loaded voltage falls below the device's operating threshold, the device may reset, stop, or fail to start.

Internal resistance is one reason for this voltage sag. Its effective value changes with the battery's discharge state, current demand, cell age, temperature, and measurement method. For battery selection, the voltage available during the device's actual current demand is more useful than a resting-voltage reading alone.

What Open Circuit and Loaded Voltage Measure

Open-circuit voltage is measured when no external current is flowing from the battery. It records the terminal voltage at rest and provides a basic reference before the device begins operating.

Loaded voltage is measured while the device is drawing current. Useful measurement points include the start of a motor load, steady operation, and the charging interval of a capacitor-based circuit.

The timing of a loaded-voltage measurement also affects the result. A reading taken immediately after the load begins can differ from one taken several seconds later. When comparing batteries, keep the load level, temperature, and measurement timing consistent.

What Internal Resistance Represents Inside an Alkaline Cell

Internal resistance is not a separate resistor installed inside a battery. It represents the combined opposition created by conductive materials, internal connections, ion movement, and electrochemical reactions within the cell.

Some voltage loss appears immediately when current begins to flow through the battery's conductive paths. During longer loads, slower electrochemical processes can create additional polarization, further affecting the terminal voltage.

Estimating Voltage Sag from a Load Step

For a defined current change, an initial voltage-sag estimate can be calculated with:

ΔV ≈ ΔI × Reff

Vafter ≈ Vbefore − ΔV

For example, if current increases by 0.50 A and effective resistance is 0.20 ohm:

ΔV ≈ 0.50 A × 0.20 Ω = 0.10 V

If terminal voltage before the load step is 1.50 V, estimated voltage after the step is approximately 1.40 V.

These figures are illustrative engineering values rather than Tiger Head product specifications. In product evaluation, you can apply the same calculation to test results collected from candidate cells under a defined load step.

How Series Connected Cells Affect Pack Voltage

Many toys and portable devices use two or more AA or AAA batteries connected in series. In this arrangement, cell voltages add together, but effective internal resistance also accumulates:

Rpack = R₁ + R₂ + … + Rₙ

Cell-to-cell consistency also matters in a series pack because the same current passes through every cell. One cell with a substantially lower operating voltage can limit pack performance even when total pack voltage initially appears acceptable. Pack evaluation should therefore record both total voltage and individual cell voltage during operation.

Separating Cell Resistance from Contact and Holder Losses

Not all voltage loss inside a device comes from the battery cells. Battery springs, metal tabs, wires, connectors, and PCB traces also add resistance to the current path. Weak spring pressure, oxidized surfaces, or undersized conductors can increase this external loss.

To locate the source, measure voltage directly across the battery pack terminals and at the device power input:

Vconnection loss = Vpack terminals − Vdevice input

If pack-terminal voltage remains stable while device-input voltage falls, the battery holder or connection path requires attention. If both readings decline by a similar amount, the cells account for most of the observed loss.

This separation prevents contact problems from being incorrectly attributed to battery performance and helps engineering teams decide whether to change the cell specification or improve the device's electrical connections.

What the Tiger Head 3.9 Ohm External Load Discharge Test Shows

Tiger Head's official dry battery catalogue provides continuous-discharge results for LR6/AA and LR03/AAA alkaline batteries under the catalogue's stated common test condition of a 3.9 ohm external load, operating 24 hours per day to a 0.9 V endpoint.

The published 3.9 ohm value refers to the external test load, not the battery's internal resistance. The table reports manufacturer-published results under that stated condition, not resistance values for use in a voltage-sag calculation.

Each result applies only to its named catalogue entry and must not be transferred between the LR6/AA, LR03/AAA, G-series or A+ products. The catalogue results shown here do not apply to the A+ LR6/AA product.

Why Regulated Electronics Can Intensify Voltage Sag

A simple resistive load normally draws less current as its supply voltage decreases. Regulated electronic circuits can behave differently because the power converter attempts to maintain a stable output for the downstream circuit.

As battery input voltage declines, the converter may draw more input current to maintain the required output power. That increase creates a feedback effect: higher current increases internal losses, and the reduced input voltage prompts the converter to demand even more current.