How to Calculate Parallel Battery Circuits

Two batteries wired in parallel provide the same voltage as one battery, but have twice the power.

If two or more identical-voltage batteries are wired together in parallel, these batteries can serve as a high-current power supply. Connecting the batteries in this fashion creates a single battery pack that can provide more power to an electrical device than one battery alone. Calculating the total power of such a battery circuit requires that you know what the power value of each battery is. Power is typically expressed in watts; however, the power value of each battery can be calculated if you know the amp-hour rating of a battery.

Things You'll Need

• Calculator
• Pen or pencil
• Paper
• Power values of 2 or more identical-voltage batteries

Instructions

1. Write down the voltage and power values of both batteries. If the batteries are rated in amp-hours or milliamp-hours (often expressed as "Ah" or "mAh"), multiply the voltage by the amp-hour rating.

2. Add together the power ratings of each individual battery.

3. Verify that the device you wish to use this battery pack for requires a power rating less than or equal to the total power rating of the battery pack.

Tips & Warnings

• When calculating power output using the amp-hour value, remember that the battery pack will provide power for approximately one hour at that rate. The battery pack will last longer in proportion to the amount of power the device requires. For example, if the device requires half of the rated power of the battery pack, the device can be operated for two hours.

References

• "Principles of Electric Circuits"; Thomas Floyd; 1996
• Sinclair Community College: Parallel Circuits
• Stanford University: Watt's Law