Batteries, Cells, and Capacitors Explained

Watch Cells, Batteries, and Capacitors Explained

Created 08-05/2002

This page attempts to explain, in layman's terms the difference between cells, batteries, and capacitors when used as a power source for quartz watches.

The Cell
Cutaway of Button CellA cell is the smallest unit of electrical storage power.

Cells consist of an assembly of 2 dissimilar metals in a chemical electrolyte.

The 2 metals are referred to as the Anode (positive pole "+") and the Cathode (Negative pole "-").

The action of the electrolyte dissolving the Cathode creates electrical current which is used to power the watch.

Once the Cathode is used up the cell is said to be "discharged" and is replaced with a new one.

Watch cells are available in many types:
Alkaline
Silver Oxide
Lithium
Rechargeable (Nicad or Manganese Titanium)
Mercury (used in early electronic watches like Accutron. Not used anymore because of environmental concerns).
 
Advantages
Long life at a stable voltage
Large power density relative to size allows many complications (stopwatches, timers, alarms, digital displays, backlights, etc.).
Long time between service intervals (for rechargables).
 
Disadvantages
Need to replace at intervals from 1 to 10 years (dependant upon type)
Older models may burst if not replaced on a timely basis causing corrosion and possible damage to the watch.
If you have a watch which uses an unusual cell finding a replacement may be difficult.
The Battery
6V battery made up pf 4 1.5v cellsA battery is simply an assembly of 2 or more cells connected in series to provide a voltage which is the sum of the voltage of the cells.

Batteries are seldom used in watches since most quartz watch movements operate on 1.5 volts (or less).

The clue as to whether a watch uses a cell or battery is in the voltage.
If the voltage is a multiple of 1.5 volts (like 3 volts) then the watch uses a battery.

Almost no watches use a battery.

The Capacitor
Platr Type Electrolytic CapacitorShown at left is a cutaway of an electrolytic capacitor of a type which could be used in a watch.

The capacitor differs from a cell or battery in that it can only store an electric charge applied to it. A capacitor does not produce electricity by chemical action.

A large number of metal plates (green) are separated from each other by plastic insulators. Enough plates are used to produce the required voltage (usually 1.2 volts).

The charging mechanism of the watch applies an electric charge to the plates which are capable of storing more energy than the watch uses in a certain amount of time.

When the watch is not charging the capacitor the remaining charge inside the capacitor is used to power the watch.

Capacitors may be:
Electrolytic Plate type (shown)
Tantalum Powder (not shown)
 
Advantages
The theoretical advantage of a capacitor is that it should never wear out since there is no electrolyte to consume the Cathode. A capacitor should be capable of being charged and discharged indefinitely if operated within temperature and voltage specifications.
 
Disadvantages
The disadvantage of a capacitor is that it has relatively little power density for it's size, and due to leakage will not hold a given voltage as long as a cell or battery. Due to the lack of power compared to a chemical cell, capacitor powered watched usually do not have a lot of complications (stopwatch, timer, digital display, backlight, etc.).

The Seiko Kinetic line of watches uses a capacitor as a power source.

Back to Main Page

E-mail your comments or questions.

1