Cells and Batteries

4.4. Cells and Batteries#

4.4.1. Cells#

A cell is the basic unit that stores chemical energy and converts it into electrical energy.

  • Every cell has a positive terminal (+) and a negative terminal (-).

  • Inside, chemical reactions release electrons, which flow through an external circuit when connected.

A standard AA battery is actually a single cell that produces about 1.5 V.

Tip

A standard AA “battery” is actually a single cell that produces about 1.5 V.

4.4.2. Types of Cells#

Alkaline (non-rechargeable)#

  • Common AA, AAA, 9V cells.

  • Cheap, widely available, but cannot be reused once flat.

NiMH (Nickel-Metal Hydride Rechargeable)#

  • Often rated at 1.2 V per cell (slightly lower than alkaline).

  • Can be recharged hundreds of times.

Lithium-ion#

  • High energy density.

  • Each cell typically around 3.6-3.7 V.

  • Can deliver high currents but require careful charging for safety.

  • Low self-discharge compared to NiMH meaning they hold charge for longer during storage.

  • Can be recharged thousands of times.

4.4.3. Batteries#

A battery is one or more cells connected together. By combining cells, we can increase the voltage or the capacity of the power supply. Series vs Parallel Connections

Series#

When cells are connected in series, end-to-end, their voltages add up. The current capacity stays the same as one cell.

Example: Three AA cells (1.5 V each) in series = 4.5 V total.

Parallel#

When cells are connected side-by-side, the voltage stays the same, but the capacity (mAh) adds up. This gives longer run time at the same voltage.

Example: Two AA cells (1.5 V each, 1200 mAh each) in parallel = 1.5 V total, but 2400 mAh capacity.