PRACTICAL TECHNIQUES & KNOW-HOW FOR MAKING & MEASURING IN THE LABORATORY & WORKSHOP

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A Comparison of Primary Battery Performance using a Solartron 7150plus Multimeter

Manufacturers' titles for their batteries use ever-increasingly inflated language to persuade the buyer that their product will outpace the competition and deliver higher currents for longer. They are "Extra Heavy Duty", "Plus", or "Ultra", and the prices can often match the superlatives used to describe them. In this brief study, the author took 13 popular brands of AA primary cells, and discharged them under controlled conditions, measuring their terminal voltages continually during the discharge process. The results enabled calculations of parameters which defined the actual performance of the batteries.

The Batteries under Study

The 13 batteries tested, pictured above, were all brand-new, with use-by dates of 2017. Table 1 gives the manufacturers' quoted data for each battery:

MANUFACTURERCODENAMETYPEPRICEFORRRPQuoted Capacity
    GBP GBPmAHrs
JCBAAR6ZincZinc/Carbon2.29010 1100mAh
JCBAALR6Super Alkaline Alkaline1.50010 2300mAh - 2850mAh
DuracellAA/LR6ProcellAlkaline4.50010 230mAh - 2850mAh
DuracellAA/MN1500Duracell PlusAlkaline2.4904.0004.1002300mAh - 2850mAh
EnergiserAA/L91Ultimate Lithium Lithium6.7304+28.6902900mAh
EnergiserAA/LR6High TechAlkaline3.4904+2 2300mAh - 2850mAh
EnergiserAA/LR6Ultra plusAlkaline1.99044.9502300.0mAh - 2850.0mAh
GP BatteriesAA Ultra Alkaline Alkaline2.4908+4 2300.0mAh - 2850.0mAh
GP BatteriesAA/R6Greencell Zinc0.90041.4901100mAh
EverreadyAA/R6Silver Zinc1.39042.0901100.0mAh
EverreadyAA/LR6Gold Alkaline1.65043.4502300.0mAh - 2850mAh
PanasonicAA/LR6Power BronzeAlkaline2.91010 2300mAh - 2850mAh
PanasonicAAEvoltaAlkaline2.6504 2300mAh - 2850mAh

Measuring the Performance of the Cells

The experimental set up used to gather the data on the AA cells is shown in the diagram above. The battery under test was discharged through a resistance box set for 30 ohms resistance. This gives an initial current flow from the cells of about 50 mA and was chosen to reflect realistic usage of the batteries and to give a discharge period of about 2 - 4 days. The terminal voltage was monitored using a Solartron 7150plus digital multimeter, coupled to a computer via a National Instruments GPIB-232 CT-A Controller. This latter device was controlled by DrKFS.net software described and available here. A short period was allowed for the monitoring of the terminal voltage of each cell before the load was applied. This enabled a calculation of the initial internal resistance of each cell to be calculated

The plot below shows the voltage profiles with time obtained for each battery.

The battery selection represents three types of dry-cell technology: Zinc-Carbon, Alkaline, and Lithium.The data above resolves well between the three types. The total area under each curve is proportional to the capacity of the cells is mA-hrs. The three curves with least area under them, correspond to the performance of Zinc-Carbon batteries. The main group of curves with larger areas beneath them are all from Alkaline cells. The curve with the highest voltage and largest area corresponds to a Lithium cell. The plots demonstrate clearly that Alkaline cells have a great advantage over Zinc-Carbon, and that they all perform similarly: no one manufacturer has any clear edge over another. This is particularly true in the useful region of the cells' life (i.e the period from the start to the point where the battery voltage falls below 1.0 volts.).

Electrical Characteristics

Using the gathered data, the electrical data in the two tables below were calculated

MANUFACTURERNAMEMaxCurrent Initial Int RInitial V
  mA ohmsvolts
JCBZinc254.1591.470
JCBSuper Alkaline50002.9661.482
DuracellProcell50003.0031.471
DuracellDuracell Plus50002.9501.470
EnergiserUltimate Lithium50005.9841.509
EnergiserHigh Tech50001.9711.483
EnergiserUltra plus50002.0891.504
GP BatteriesUltra Alkaline50002.5161.482
GP BatteriesGreencell254.0411.440
EverreadySilver 253.2241.495
EverreadyGold 50002.9601.470
PanasonicPower Bronze50002.2101.493
PanasonicEvolta50001.9951.494

Above: Quoted maximum current, internal resistance, Initial terminal voltage for each cell.

MANUFACTURERNAMECODETotal mAhrTotal EnergyUsable mAHrUsable Energy
   mAHrsjoulesmAHrsjoules
JCBZincAAR6117742938073570
JCBSuper AlkalineAALR630081185022159580
DuracellProcellAA/LR6325612769242310521
DuracellDuracell PlusAA/MN1500335012770235210179
EnergiserUltimate LithiumAA/L91339516083313915798
EnergiserHigh TechAA/LR6323912614235710336
EnergiserUltra plusAA/LR6334313014253511130
GP BatteriesUltra AlkalineAA 31181189321399328
GP BatteriesGreencellAA/R696136016943036
EverreadySilver AA/R6124145138403711
EverreadyGold AA/LR628531117421699372
PanasonicPower BronzeAA/LR6302712218237210435
PanasonicEvoltaAA308712591247410833

Above: Total mA-hrs, total energy, usable mA-hrs, usable energy fro each cell

The tables show that the internal resistance of the Zinc Carbon cells was about 4 ohms and consistently higher than that of the alkaline cells at about 2-3 ohms. Among the alkaline cells, those boasting some superior performance did have lower internal resistances down to 1.9 ohms and this probably is the basis for their superior current delivery. The Lithium cells appear to have a high internal resistance which is partly compensated for by a higher terminal voltage.

The usable mA-hr output, (i.e. the output before the voltage falls below 1 volt.) is about 2/3rds of the total output. Clearly the manufacturers' quoted output is based upon the total output not the usable output. The data shows the alkaline cells to provide an output 3 times greater than the zinc-carbon, while the Lithium cell provides some four times as much. But it is in terms of energy, that the Lithium cells are most shown to excel. Owing to the higher terminal voltage, the Lithium cell generated 4 times as much energy as the Zinc cells, while the alkaline cells generated three times as much.

Voltage Constancy

Constancy of terminal voltage from dry cells is not as important as it once was. Sophisticated voltage regulation is now readily available and it is possible to use energy from batteries in more discharged state than previously. However there can be occasions when voltage constancy is an important feature, particularly as mercury cells (which had very high voltage constancy) are no longer available. The table below shows the average slope of the terminal voltage with mA-hr and energy output during discharge across the useful life of the cells.

MANUFACTURERNAMEV decay/maHrV decay/joule
  mV/mAHrmV/joule
JCBZinc0.5830.132
JCBSuper Alkaline0.2180.050
DuracellProcell0.1940.045
DuracellDuracell Plus0.2000.046
EnergiserUltimate Lithium0.1620.032
EnergiserHigh Tech0.2050.047
EnergiserUltra plus0.1990.045
GP BatteriesUltra Alkaline0.2250.052
GP BatteriesGreencell0.6340.145
EverreadySilver 0.5900.133
EverreadyGold 0.2170.050
PanasonicPower Bronze0.2080.047
PanasonicEvolta0.2000.046

As may be expected, the lowest slope (and therefore highest constancy) is exhibited by the Lithium cell, followed by the Alkaline. Highest decay rates were exhibited by the Zinc-Carbon cells.

Cost

Using the price data above, the cost per unit output and energy is shown below:

MANUFACTURERNAMECODEUNIT PRICECost per usable mAHrCost per usable JouleMANUFACTURER
    pence/maHrpence/kjoule 
JCBZincAAR60.2290.0286.414JCB
JCBSuper AlkalineAALR60.1500.0071.566JCB
DuracellProcellAA/LR60.4500.0194.277Duracell
DuracellDuracell PlusAA/MN15000.6200.0266.091Duracell
EnergiserUltimate LithiumAA/L911.1200.0367.090Energiser
EnergiserHigh TechAA/LR60.5800.0255.611Energiser
EnergiserUltra plusAA/LR60.5000.0204.492Energiser
GP BatteriesUltra AlkalineAA 0.2100.0102.251GP Batteries
GP BatteriesGreencellAA/R60.2250.0327.412GP Batteries
EverreadySilver AA/R60.3500.0429.431Everready
EverreadyGold AA/LR60.4100.0194.375Everready
PanasonicPower BronzeAA/LR60.2900.0122.779Panasonic
PanasonicEvoltaAA0.6600.0276.093Panasonic

Cost per unit usable output is highest for zinc-carbon cells and lowest for Alkaline. Cost per unit output for the Lithium cell was almost as high as that for the zinc-carbon, owing to the very high unit cost of Lithium cells.

The Best Battery

Which battery is best? It depends upon what characteristic is important for the user:
The battery with the highest usable output & energy is the Energiser, Ultimate Lithium.
The battery with the lowest internal resistance is the Energiser High Tech Alkaline.
The battery with the most stable voltage output is the Energiser Ultimate Lithium.
The battery with the lowest energy cost is the JCB Super Alkaline.