Master the Basics: Batteries in series and parallel

When building a battery-powered circuit, sometimes a single battery doesn’t provide enough voltage or capacity to meet your needs. That’s where combining batteries in series, parallel, or both comes in. Many everyday devices—like remote controls—use multiple batteries for this exact reason.

Batteries in Series: More Voltage

To increase voltage, connect batteries in series. This means linking the positive terminal of one battery to the negative terminal of the next.

Example: Two AA batteries (1.5V each) in series = 3V total

Think of it like stacking voltages—each battery adds its own voltage to the total.

Key points:

• The total voltage is the sum of all battery voltages.

• The same current flows through all batteries.

• Capacity (mAh) stays the same as a single battery.

Adding more batteries in series will increase voltage, and based on Ohm’s Law, that can result in more current—but each battery still provides the same amount of energy as it would alone.

Batteries in Parallel: More Capacity

To increase capacity or extend run-time, connect batteries in parallel. This means connecting all positive terminals together, and all negative terminals together.

Example: Two AA batteries in parallel still provide 1.5V, but the capacity doubles. If each battery has 2400 mAh, the total becomes 4800 mAh.

Key points:

• Voltage remains the same.

• Capacity adds up.

• Batteries share the current load, so each one works less and lasts longer.

• Higher current output is possible, which can be useful for powering bigger loads.

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Parallel + Series: Best of Both Worlds

You can also combine batteries in both series and parallel to increase both voltage and capacity.

Example: Six AA batteries arranged as three parallel sets of two series-connected batteries.

• Output Voltage = 3V (1.5V + 1.5V per series pair)

• Capacity = 7200 mAh (2400 mAh × 3 parallel stacks)

• Current Output = 150 mA (50 mA × 3)

This setup is common in battery packs for devices that need more power and longer battery life.

Important Tips for Combining Batteries

• Always use batteries of the same type (e.g., all alkaline or all lithium).

• Only combine batteries with the same charge level or freshness.

• Mixing old and new batteries can lead to uneven discharging, overheating, or reduced performance—especially in parallel.

Key Takeways

Understanding how to combine batteries in series and parallel lets you customize power sources for different projects. Need higher voltage? Go series. Need longer run-time or more current? Go parallel. Need both? Combine the two. Just make sure to use matching batteries for safety and efficiency.

Whether you're powering a sensor, robot, or flashlight, this knowledge helps you build smarter, more reliable circuits.