Better Use Of Batteries V1.00

• About the Author
• Introduction
• Battery Codes
• Battery Characteristics
• Cell Types
• Closing Comments

Author: Martin Hillier
E-Mail: Martin@hillier.demon.co.uk
Updated: 9/5/1995
Revision: 1.0

   Battery      Voltage      Codes

  =========    =========    ===================================

   N            1.5V         UM5, Lady

   AAA          1.5V         HP16, UM4, LRO3, MN2400, Micro

   AA           1.5V         HP7, UM3, LR6, MN1500, Mignon

   C            1.5V         HP11, UM2, LR14, MN1400, Baby

   D            1.5V         HP2, UM1, LR20, MN1300, Mono

   PP3          9.0V         6F22, E-Block, MN1604, 1604, 006P,

                             6R61, Neda

Capacity

This can be defined as how much a cell can supply and for how long. The useful life of a 1.5V cell is over when they drop below a certain threshold, 0.9V. Battery Capacities (Ah)

     Type >     Zinc Carbon    Zinc Chloride    Alkaline Magnesium

Size

====           =============   ==============  ===================

N                                               0.5

AAA                             0.54            0.7

AA              0.9             1.1             2.3

C               1.8             2.8             7

D               5.2             7.5             14

PP3             0.3             0.4             0.5



     Type >     Standard        Industrial      Nickel Metal

Size            Ni-Cad          Ni-Cad          Hydride

====           =============   ==============  ===================

N               0.15

AAA             0.22

AA              0.5             0.85            1.2

C               1.6             2.0

D               1.2             4.0

PP3             0.12

Internal Resistance

All cells have some internal resistance. As cell sizes increase there internal resistance decreases, due to larger conducting surfaces. As cells become discharged the resistance also rises, so a cell which has failed in a high current application will still work for some time in a lower current application. Lower internal resistance means longer life and higher current.

Shelf Life

Cells discharge and decay when left standing, it is defined as the time taken for a cells capacity to fall to 85% of the original. Applications which take little current like smoke alarms, will often use the battery for over a year and failure can be due to the time it has been used for and not the current drawn.

Zinc Carbon

These are the cheapest cells available and have changed very little since there invention in 1860.

There internal resistance is quite high and can not supply much current, they have a high shelf life and also decay when used. As the Zinc can is also the anode, they are prone to leaking if the Zinc fails to oxidise evenly. Leaking can also occur if they are over discharged.

They are best suited to low power applications with intermittent use, say a small radio for an hour or so a day. Zinc Carbon needs frequent rests to recover and are not suitable for continuous use. Don't use these cells in expensive equipment or leave them in equipment for long times, because of the risk of leakage. Stand-By applications and wide temperature ranges should also be avoided.

Zinc Chloride

These are improved versions of Zinc Carbon, with the Chloride electrolyte. This causes the cell to dry out as it is used, reducing the risk of leakage.

They tend to have lower internal resistance and higher capacities, allowing higher currents to be drawn for longer periods. The longer shelf life is a major factor in buying these cells.

Zinc Chloride cells are suited to moderate intermediate use, as in cycle lights where performance is close to Alkaline cells. They work well with lower power applications such a clocks, although they are not suited to Stand-By usage where they will be unused for long lengths of time.

Alkaline

During world war 2 the need for better cells was realised. The Alkaline cell was the answer, producing higher currents for long periods, reliable cells with a long shelf life and they could perform under a wide range of temperatures.

The Alkaline Potassium Hydroxide electrolyte rather than the acidic electrolyte in Zinc cells gives them there name.

There low internal resistances gives higher performance, in applications such a camera flashlights where Zinc cell don't work. The components are enclosed within a separate steel can, giving good leak resistance.

The key to Alkaline tests is the continuous nature, the high power and heavy use is needed to get the most out of these cells, in intermittent low power applications they only give about 2 to 3 times the capacity of Zinc Carbon. These cells don't work well in continuous low power applications.

Lithium

The reactive nature of Lithium to air give these cells there high shelf lifes, which are measured in decades. They can with stand high temperature variations and are virtually leak proof.

They are ideal for low drain applications such as smoke alarms and data retention. The high price is justified with a very long life.

Nickel Cadmium

The capacity of these cells is around one fifth of Zinc Carbon cells, they also discharge on standing, cells charged some time ago may be flat by the time you want to use them. This means they are not suited to lower drain applications.

The basic voltage for Ni-Cads is 1.2V which makes them unsuitable for certain applications. The number of times they can be recharged is also limited, bad charging habits reduce this even more.

They do have fantastically low internal resistance which gives very high currents, this can also come in useful for starting fires.

The main problem with Ni-Cads is the dendrite growths, miniature metal spikes which eventually short circuit the cell. This can be reduced by PCR charging.

Nickel Metal Hydride

This newer rechargeable cell is free from toxic elements such as cadmium, they have around 30 to 50% more capacity than good Ni-Cad cells. They cost about twice as much as Ni-Cads, but have a shorter service life, up to 1000 cycles compared with 3000.

Because there is no Cadmium in the formulation, there is no memory effect and is useful in plug in rechargeable tools and lights.

When ever possible use mains adapters, its 5000 times cheaper than batteries.