*Question T4A09:
How can you determine the length of time that equipment can be powered from a battery?*  

*Correct Answer is  B: Divide the battery ampere-hour rating by the average current draw of the equipment*  

### AI Response: (may contain errors)  

To determine how long equipment can be powered from a battery, the correct approach is to divide the battery's ampere-hour (Ah) rating by the average current draw (in amperes) of the equipment. This is represented by the formula:

$$
\text{Time (hours)} = \frac{\text{Battery Ah rating}}{\text{Average current draw (A)}}
$$

### Explanation of the Correct Answer (Choice B):
- **Choice B** is correct because it directly relates the capacity of the battery (in ampere-hours) to the current consumption of the equipment. 
- If a battery has a rating of, say, 100 Ah and the equipment draws 10 A, the time the equipment can run is:

$$
\text{Time} = \frac{100 \text{ Ah}}{10 \text{ A}} = 10 \text{ hours}
$$

### Why the Other Choices are Incorrect:
- **Choice A**: "Divide the watt-hour rating of the battery by the peak power consumption of the equipment."
  - This choice is incorrect because it uses watt-hours (Wh) instead of ampere-hours (Ah). While it could work if you convert the power to current, it is not the most straightforward method for this question.

- **Choice C**: "Multiply the watts per hour consumed by the equipment by the battery power rating."
  - This choice is incorrect because it suggests multiplying rather than dividing. The relationship between power (watts) and current (amperes) is not correctly applied here.

- **Choice D**: "Multiply the square of the current rating of the battery by the input resistance of the equipment."
  - This choice is incorrect because it introduces unnecessary complexity and does not relate to the time calculation. The square of the current and input resistance does not provide a meaningful measure of battery life.

### Useful Formulas and Rules of Thumb:
- To convert watt-hours to ampere-hours, use the formula:

$$
\text{Ah} = \frac{\text{Wh}}{V}
$$

where $V$ is the voltage of the battery. 

- Always ensure that the current draw is averaged over time, as equipment may not draw a constant current.

By understanding these concepts, you can effectively determine how long your equipment can run on a given battery.