How much internal resistance would a 12V NiMH battery possess if it is nearly completely dead, i.e., possessing almost zero amp-hour capacity?

When a NiMH battery is nearly completely discharged and has almost zero amp-hour capacity remaining, its internal resistance typically increases significantly compared to when it's fully charged. Internal resistance in batteries generally decreases as the state of charge increases because more ions are available to conduct current.

For a 12V NiMH battery that is nearly dead (essentially zero capacity remaining), the internal resistance could be quite high. Exact values can vary based on the specific battery chemistry, design, and condition, but it could range from several ohms to tens of ohms.

High internal resistance in a nearly dead NiMH battery occurs because:

1. Depletion of Electrolyte: As the battery discharges, the availability of ions in the electrolyte decreases, reducing the conductivity within the battery.
2. Formation of Passivation Layers: Certain chemical processes during discharge can lead to the formation of passivation layers on electrodes, which can increase resistance.
3. Physical Changes: Structural changes within the electrodes and separators as the battery discharges can also contribute to increased resistance.

In practical terms, high internal resistance in a nearly dead NiMH battery means it can no longer deliver sufficient current effectively, which is why such batteries may fail to power devices even if they have some residual voltage.