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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 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:
|JCB||AALR6||Super Alkaline||Alkaline||1.500||10||2300mAh - 2850mAh|
|Duracell||AA/LR6||Procell||Alkaline||4.500||10||230mAh - 2850mAh|
|Duracell||AA/MN1500||Duracell Plus||Alkaline||2.490||4.000||4.100||2300mAh - 2850mAh|
|Energiser||AA/LR6||High Tech||Alkaline||3.490||4+2||2300mAh - 2850mAh|
|Energiser||AA/LR6||Ultra plus||Alkaline||1.990||4||4.950||2300.0mAh - 2850.0mAh|
|GP Batteries||AA||Ultra Alkaline||Alkaline||2.490||8+4||2300.0mAh - 2850.0mAh|
|Everready||AA/LR6||Gold||Alkaline||1.650||4||3.450||2300.0mAh - 2850mAh|
|Panasonic||AA/LR6||Power Bronze||Alkaline||2.910||10||2300mAh - 2850mAh|
|Panasonic||AA||Evolta||Alkaline||2.650||4||2300mAh - 2850mAh|
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.).
Using the gathered data, the electrical data in the two tables below were calculated
|MANUFACTURER||NAME||MaxCurrent||Initial Int R||Initial V|
|GP Batteries||Ultra Alkaline||5000||2.516||1.482|
Above: Quoted maximum current, internal resistance, Initial terminal voltage for each cell.
|MANUFACTURER||NAME||CODE||Total mAhr||Total Energy||Usable mAHr||Usable Energy|
|GP Batteries||Ultra Alkaline||AA||3118||11893||2139||9328|
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.
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.
|MANUFACTURER||NAME||V decay/maHr||V decay/joule|
|GP Batteries||Ultra Alkaline||0.225||0.052|
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.
Using the price data above, the cost per unit output and energy is shown below:
|MANUFACTURER||NAME||CODE||UNIT PRICE||Cost per usable mAHr||Cost per usable Joule||MANUFACTURER|
|GP Batteries||Ultra Alkaline||AA||0.210||0.010||2.251||GP Batteries|
|GP Batteries||Greencell||AA/R6||0.225||0.032||7.412||GP Batteries|
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.
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.