Choices of Primary Batteries

Early batteries were used mainly for experimental purposes. Voltages fluctuated under load and made them impractical for most applications. In 1836, John F. Daniell, an English chemist, developed an improved battery that offered more stable current delivery and was suitable to supply power to telegraph networks since electrical distribution networks did not exist at the time. These early batteries were non-rechargeable (primary) and it was not until 1859 when the French physician Gaston Planté invented the first rechargeable battery based on the lead acid chemistry. Read more about When Was the Battery Invented?

Carbon-zinc, also known as the Leclanché battery, was one of the first commercial batteries. The early Leclanché cell in 1876 was wet, and the dry cell was developed in 1886. The first consumer carbon-zinc batteries for flashlights appeared in 1898, a development that formed the Eveready battery company. Carbon-zinc is the least expensive battery and normally comes with consumer devices when batteries are included. These general purpose batteries are used for low power drain applications, such as remote controls, flashlights, children’s toys and wall clocks.

One of the most common primary batteries for consumers is the alkaline-manganese, or Alkaline for short. Lewis Urry invented the Alkaline in 1949 while working with the Eveready Battery Company Laboratory in Parma, Ohio. Alkaline delivers more energy at higher load currents than carbon-zinc and it does not leak when depleted, although it is not totally leak-proof. A discharging Alkaline generates hydroxide gases. Pressure buildup can rupture the seal and cause corrosion in form of a feathery crystalline structure that can spread to neighboring parts and cause damage. All primary batteries produce gas on discharge. Portable devices with these batteries must have provision for venting. 

Lithium Iron Disulfide (Li-FeS2) is a newcomer to the primary battery family and offers improved performance. Lithium batteries normally deliver 3 volts and higher, but Li-FeS2 produces 1.5 volts to serve as an alternative of alkaline and carbon-zinc in the AA and AAA formats. It has a higher capacity and a lower internal resistance than Alkaline. This enables moderate to heavy loads and is ideal for digital cameras. Further advantages are improved low temperature performance, superior leakage resistance and low self-discharge, allowing 15 years of storage at ambient temperatures. Low weight and minimal toxicity are added benefits.

The disadvantages of the Li-FeS2 are a higher price and transportation issues because of the lithium metal content in the anode. This causes restriction in air shipment. In 2004, the US DOT and the Federal Aviation Administration (FAA) banned bulk shipments of primary lithium batteries on passenger flights, but airline passengers can still carry them on board or in checked bags. Each AA-sized Li-FeS2 contains 0.98 grams of lithium; the air limitation of primary lithium batteries is 2 grams (8 grams for rechargeable Li-ion). This restricts each passenger to two cells; however, exceptions are made and 12 batteries can be carried as samples. Read more about How to Transport Batteries.

The Li-FeS2 includes safety devices in the form of a resettable PTC thermal switch that limits the current at high temperature. The Li-FeS2 cell cannot be recharged as is possible with NiMH in the AA and AAA formats. Recharging, putting in a cell backwards or mixing with used batteries or other battery types could cause a leak or explosion. Read more about Health Concerns with Batteries.

     Figures 1 and 2 compare the discharge voltage and internal resistance of Alkaline and Li-FeS2 at a 50mA pulsed load. Of interest is the flat voltage curve and the low internal resistance of Lithium; Alkaline shows a gradual voltage drop and a permanent increase in resistance with use. This shortens the runtime, especially at an elevated load.

	Figure 1: Voltage and internal resistance of Alkaline on discharge. The voltage drops rapidly and causes the internal resistance to rise
	Figure 2: Voltage and internal resistance of Lithium on discharge. The voltage curve is flat and the internal resistance stays low Both images are courtesy of Energizer

The AA and AAA are the most common cell formats. Known as penlight batteries for pocket lights, the AA became available to the public in 1915 and was used as a spy tool during World War I; the American National Standard Institute standardized the format in 1947. The AAA was developed in 1954 to reduce the size of the Kodak and Polaroid cameras and shrink other portable devices. In the 1990s, an offshoot of the 9V battery produced the AAAA for laser pointers, LED penlights, computer styli, and headphone amplifiers. Read more about A look at Old and New Battery Packaging. Table 3 compares carbon-zinc, alkaline, lithium, NiCd, NiMH and nickel-zinc and the AA and AAA cell sizes.

	Carbon-zinc	Alkaline	Lithium (Li-FeS2)	NiCd	NiMH
Capacity*  AA                AAA	400-1,700 ~300	1,800-2,800 800-1,200	2,500-3,400 1,200	600-1,000 300-500	800-2,700 600-1,250
Nominal V	1.50	1.50	1.50	1.20	1.20
Discharge Rate	Very low	Low	Medium	Very high	Very high
Rechargeable	No	No	No	Yes	Yes
Shelf life	1-2 years	7 years	10-15 years	3-5 years	3-5 years
Leak resistance	Poor	Good	Superior	Good	Good
Retail **  AA               AAA	Not available in most stores	$0.40-2.80 $1.50-2.80	$3.00-5.00 $4.00-5.00	Not available in most stores	$4.00-5.00 $4.00-5.00

Table 3: Summary of batteries available in AA and AAA format. The capacity on the AA is double that of the AAA at similar price, making the energy storage cost of the AAA twice than that of the AA.

*    In mAh; discharge current is less than 500mA
**  Estimated prices in $US (2012)

The AAA cell contains roughly half the capacity of the larger AA at a similar price. In essence, the energy cost of the AAA is twice that of the AA. In an effort to downsize, energy cost often takes second stage and device manufacturers prefer using the smaller AAA over the larger AA. This is the case with many bicycle lights where the AA format would only increase the device slightly but deliver twice the energy for the same battery cost. Proper design considerations help protect the environment by generating less waste.

Retail prices of the Alkaline AA vary, so does performance. Exponent, a US engineering firm, checked the capacity of eight brand-name alkaline batteries in AA packages and discovered a discrepancy between the best and lowest performers of 800 percent. A practical gauge to test batteries is counting the shots a digital camera can take with a set of cells. The relatively high current pulses of a digital camera stress the battery more than a remote control or a kitchen clock would. When a regular Alkaline stops functioning in a digital camera, the remaining energy can still power a remote control and run a kitchen clock for up to two years.

Figure 4 illustrates the number of shots a digital camera can take with discharge pulses of 1.3 watts on Alkaline, NiMH and Lithium Li-FeS2 in an AA package. (Two cells put in series to get 3V, 1.3W draws 433mA.) Although the three battery chemistries tested have similar capacities, the results in form of pulse counts vary largely. The clear winner is Li-FeS2 with 690 pulses; the second is NiMH with 520 pulses and the distant third is standard Alkaline producing only 85 pulses. Internal resistance rather than capacity governs the shot count here. Read more about How to Rate Battery Runtime.

Figure 4: Number of shots a digital camera can take with Alkaline NiMH and Lithium Li-FeS2, NiMH and Alkaline have similar capacities; the internal resistance governs the shot count on a digital camera.    Li-FeS2, 3Ah, 690 pulses NiMH, 2.5Ah, 520 pulses Alkaline, 3Ah, 85 pulses Test: ANSI C18.1 Courtesy of Exponent

The rated capacity as a performance indicator is most useful at low discharge currents; at higher loads the power factor begins to play an important role. The relationship between capacity and the ability to deliver current can best be illustrated with a Ragone Chart. Read more about Calculating Battery Runtime. Named after David V. Ragone, the Ragone chart evaluates an energy storage device on energyand power.

References

Presentation by Dan Durbin, Energizer Applications support, Medical Device & Manufacturing (MD&M) West, Anaheim, CA, 15 February 2012

Presentation by Quinn Horn, Ph.D., P.E. Exponent, Inc. Medical Device & Manufacturing (MD&M) West, Anaheim, CA, 15 February 2012