Charging a 12V 2Ah Battery with a 12V 100Ah Battery: Understanding the Process

To determine how long it takes to charge a 12V 2Ah battery using a 12V 100Ah battery, we need to consider several factors, including the charging current, the efficiency of the charging process, and the state of charge of both batteries. This article will provide a detailed explanation of the calculations involved and the real-world considerations that affect the charging time.

Basic Calculation

Assuming Ideal Conditions: If we assume that the charging process is 100% efficient and that the voltage remains constant at 12V, the charging current will depend on the internal resistance and the connection method.

Current Calculation

If you directly connect the two batteries, the current can be estimated using Ohm's Law but in practice, it can vary based on the internal resistance and the state of charge of both batteries. For simplicity, let's assume a direct connection allows a current of around 1A to flow. This is a rough assumption, and the actual current may vary.

Charging Time Calculation

Assuming the charging current is 1A, we can calculate the charging time using the following formula:

[ text{Charging Time} frac{text{Battery Capacity}}{text{Charging Current}} frac{2 text{Ah}}{1 text{A}} 2 text{ hours} ]

Real-World Considerations

Charging Efficiency

Charging is typically not 100% efficient. You might lose 10% to 20% of the energy due to heat and other factors, so the actual charging time could be longer.

Battery State of Charge

If the 2Ah battery is deeply discharged, it may take longer to charge than if it were partially charged.

Current Limiting

If the smaller battery has a built-in protection mechanism or if the larger battery's internal resistance limits the current, the charging time will increase.

Conclusion

Under ideal conditions, it would take about 2 hours to charge a 12V 2Ah battery from a 12V 100Ah battery if you assume a charging current of 1A. However, due to real-world inefficiencies and variable current, it may take longer.

Additional Insights

Lead Acid Batteries: A full lead acid battery will never fully charge a discharged one, no matter how big the "full" battery is. A fully charged lead acid battery will provide 13.6V for a few minutes and will slowly drop to about 12.6 to 13.0V.

Prophets of Doom: The concerns about a "dead short" being created are incorrect because a discharged battery has a comparatively high internal resistance.