Battery Basics

In our circuits, we’ve been using a battery. Technically, we’ve been using a cell. A battery is a collection of cells in series (or may be a single cell).

In the schematic symbol for battery that we’ve referred to, we see a single primary cell represented. For a battery, we duplicate the symbol for the number of cells that are contained in the ‘battery’, until it becomes unpractical to do so, and make a symbol that has 2 cells with dots in between to indicate more cells present.

Schematic Symbol  Description  Circuit Schematic Reference
   Symbol-Cell  Battery (Specifically a cell) Battery (Specifically a cell)
 Symbol-Battery-3-cell  3 Cell battery (3 cells are shown)
 Symbol-Battery Battery with unspecified number of cells. The voltage would normally be indicated.)

AAA, AA, C and D are common cylindrical battery sizes that contain a single cell.

The number of cells within the battery depend on various factors such as battery chemistry, but this is typically 1.5V per cell.

Batteries in Series

Connecting batteries in series raises the available voltage by the number of batteries connected. Multiply the individual battery voltage by the number of batteries to get the new voltage. The batteries would be connected positive to negative and so on. Higher voltage batteries (9V, 12V, etc.) are made up of multiple cells which are internally linked in this way.

A standard rectangular 9V battery is actually a package made up of six 1.5V cells, and opening one up reveals the individual cells inside.

[Picture showing cutaway of a 9V battery showing individual cells]

Likewise, a 12V car battery is made up of eight 1.5V cells in series. 1.5 X 8 = 12 – Car batteries often have separate access to the individual cells for topping up with distilled water. Similar smaller batteries exist, used as backup batteries in equipment such as fire and burglar alarms.

[Picture showing cutaway of car battery showing individual cells]

Lithium cells are typically 3-4V (depending on their specific chemistry), so a laptop battery delivering around 11V would typically contain 3 batteries (Which may be doubled in parallel to give the same voltage and current, but double the capacity).

[Picture showing cutaway of laptop battery showing individual cells]

Batteries in Parallel

Batteries connected in parallel will provide the same voltage as a single battery, but there will be a larger capacity of power available – they can work at a higher current. Parallel connection by having a common positive connection and a common negative connection, i.e. the same polarity is connected together.

Battery Polarity

Batteries have their polarity (negative or positive) marked on the battery casing, however, batteries used in equipment that are not designed to be removed (such as those in a laptop or drill battery pack) are often unmarked. Duracell and Varta brand batteries have a gold band at the positive end, and some manufacturers copy this, however, batteries from other manufacturers such as Sony should be double-checked, as the band can sometimes be placed on the other end. Not realising this and connecting batteries the wrong way in a circuit could be undesirable. When designing circuits, it's good practice to allow for some protection against batteries that have been connected the wrong way around.