Selecting the Right Battery

The proper battery can be the difference between a successful product and a costly failure. To help you find the best battery, we have several resources, including a Specification Checklist (below), our free Technology Library, and an Engineering and Design Flowchart.

Specification Checklist

As a product is designed, the battery specifications should account for the following:

Voltage

It is important to know not only the nominal voltage, but also the minimum and maximum for the application. As an example, a 7.2 volt nominal nickel metal hydride pack will vary from 6.0 volts in a fully discharged state to 9.6 volts at the end of charge.

Discharge Current

Both the average and maximum discharge currents are needed to specify the proper battery. Most often, the average current determines how large the battery must be to operate the device for a given amount of time. But in some cases there are intermittent high loads, and the maximum current requires a larger battery for the device to operate at all.

Cycle Life

If the battery is rechargeable, the number of charges and discharges required over the life of the battery will help determine the ideal chemistry and capacity.

Service Life

For a non-rechargeable or a backup battery, the size and chemistry will be determined by the required life, as well as the discharge and temperature profiles.

Cost

A technically ideal battery could be cost prohibitive. Note, however, that a more expensive battery can sometimes pay for itself several times over in the form of reduced replacement costs and/or better performance.

Charging

Improper charging is the leading cause of early failure in rechargeable batteries. A better charger will often pay for itself in increased performance and reduced replacement costs.

Self Discharge

This is a measure of how quickly a cell will lose its energy while sitting on the shelf. Note that higher temperatures will significantly reduce the shelf life of any battery.

Primary Batteries:

Carbon . . . . . .	2.5 years
Alkaline . . . . .	5 years
Lithium . . . . . .	10+ years

Rechargeable batteries:

Lead acid . . . .	6 months between "top off charges"
NiCds . . . . . . .	1 year between charges
NiMH . . . . . . .	1 year between charges
Lithium . . . . . .	1 year between charges

One-Time-Use or Rechargeable

One-time-use or primary cells, once discarded must be replaced with a fresh battery. Rechargeable or secondary cells can be used many times, but require a charger.

Storage

• Duration - Consider not only inventory turnover, but how long the batteries will spend in the supply chain and in your customer's inventory before being used or recharged.
• Conditions - What temperature and moisture conditions will your battery be stored under?

Weight & Dimension

Cells of various chemistries are made in a wide variety of sizes, and custom battery packs offer even more flexibility. Note that a smaller, lighter battery with the same energy usually costs more than a larger, heavier one, and even if money is no object, there is a limit to how small and light a battery can be.

Temperature

If your product will be used or stored in hot or cold conditions, battery performance and life could be affected. Low temperatures compromise performance, while high temperatures dramatically reduce the life of cells.