Battery FAQ

Primary or Secondary?

Primary cells are "one time use" batteries. Once the chemical reaction takes place, the cell loses its ability to produce energy; it is then discarded and replaced with a fresh cell or battery.

Secondary batteries are "rechargeable," and the chemical reaction that takes place within the cell is reversible and repeatable for perhaps thousands of times depending on the chemistry.

Cost?

Low cost is often thought of as the biggest factor when selecting a battery type. We would all like to see a battery the size of a finger nail with thousands of ampere hours of capacity and be able to download it for free off the Internet. The reality is, however, that many times a higher initial battery cost pays for itself in long term benefits. Low cost is not always best.

Weight?

The evolution electronics devices are also consistently driving the weight down. Batteries are also often the heaviest component in a portable electronic device.

Carbon based batteries are lighter than alkaline with less performance. Lithium cells are lighter than other primary chemistries and have superior shelf life and performance.

Li-ion and lithium polymer chemistries are far lighter than other rechargeable batteries the same size and have improved he portability of many electronic devices.

Temperature?

Temperature is an often overlooked aspect of battery performance. It is, however, a major consideration when selecting a battery. Batteries do not charge or discharge well at low temperatures. High temperatures are detrimental to shelf life (self-discharge). Most batteries perform best in the 20° C to +60° C range.

Lithium primary cells do better than most chemistries at both temperature extremes.

Some lead acid batteries, such as Bolder TMF, do well at -40° C, and there are special "high temp" NiCds that are designed to perform at +70° C.

Drain Rate?

How fast will your battery be used up? Will the load be m amperes, or will it be 10 to 50 ampere loads or more? Lithium coin cells do well at low load, long term rates. Lead acid and NiCd are good choices for high rate applications.

A battery may be discharged under different modes depending on the equipment load. The type of discharge mode selected will have a significant impact on the service life delivered by a battery in a specified application. Three typical modes under which a battery may be discharged are:

• Constant Resistance ("R"): In this mode, the resistance of the equipment load remains constant throughout the discharge.

• Constant Current ("C"): In this mode, the current drawn by the device remains constant during the discharge.

• Constant Power ("P"): In this mode, the current during the discharge increases as the battery voltage decreases, thus discharging the battery at a constant power level (Power = Current x Voltage).

Charge rate?

If your battery is a secondary type, how fast do you need to recharge it? Lead acid (C/300) and some NiCds (C/20 to C/30) do well on float or trickle charges for "stand by" applications. A 14 hour charge (C/10) is considered "standard" for sealed lead acid, NiCd, and NiMH batteries. Seven hour fast charges are possible for most secondary chemistries. If you require a rapid charge of one hour or less NiCd or Bolder TMF are good choices. Li-ion and lithium polymer batteries require a special two charge that usually takes three hours to complete.

Self Discharge?

A battery is said to be "no good" when can not deliver a least 80% of its rated capacity. How quickly will a cell loose its energy just sitting on the shelf? Primary batteries will last for years.

Carbon cells last about two to three years; Alkalines will last five years, and lithium can last ten years or more.

Rechargeable or secondary batteries loose there charge when in storage. Lead acid batteries will last about six months between "top charges." NiCds last about 30 days to 80% capacity. NiMH cells loose their charge in two to three weeks and lithium rechargeables can sit for several months.

Note: High ambient temperature will reduce the shelf life of all batteries, perhaps significantly.

Recycling?

Currently, the only two chemistries that must be recycled by law are lead acid and NiCd. These batteries must be clearly marked with the "chasing arrows" symbol and a national 800 phone number that end users may use to locate their local recycling center.