BATTERY REVIVAL

Alkaline battery are supposed to be single use equipment .However it is well known  that  they can be recharged several time ans it is even possible to buy  equipement to do it .Due to the high price of the KW.H given by this  type of battery(around 1000 more expensive than electricity coming from  electric power plant )  it is obvious that there is a great incentive  to extend their  life time .However it is not easy to find out over the net experimental results in the conditions used with the equipment using these batteries .In some case (like for remote control or electronic clock ) the consumption is low  in some other case it is the opposite .In my own case  the average consumption in use is in the range of 10 to 30 mA  and that why i decide to make my own testing in this AMP range so as to estimate how many time i will be able to recharge standard alkaline battery  and even rejuvenate junk battery  using  (thanks to EDF ) atomic electrcity at 0.10 euros /kwh . The experiments were made using varius  standard  AA alcaline battery .This type of battery  have a capacity in the range of 2 Amp.hour depending in a large extent of the discharge current . The set up used for the test  consist of a microcontroller switching the battery either to a constant current power supply for loading   or to a resistor for the discharge .The voltage  across the battery is measured as the current flowing in the battery .These data , measured with a 12 bit A/N  circuit every 15 minutes  are stored ,  thanks to a PC collecting them for further use  .A typical cycle is as followed :    * settling time of  30 mn with no current to measure voltage      * charging at constant current during  X hours      * settling time of  30 mn with no current to measure voltage       * discharge down to a given voltage across the battery       * settling time of  30 mn with no current to measure voltage The process is repeated as many times as desired . As stated earlier the capacity of a battery depend on a large extend of the discharge rate .This discharge rate an be quite different from a battery feeding a clock  or for a battery feeding a radio transmitter with a lot of cases in between .In our own case the discharge current is generaly in the range of 20 to 40 mA  and all experiments were dons in that range The data collected by the PC were plotted using GNUPLOT a versatile ploting program

schematic of experimental set up	The real setup

TEST OF A BRAND NEW BATTERY (LEKIUM) A saline battery (Brand name LEKIUM )  bought  in a local department store was tested  at a discharge rate near 40 ma until the voltage  across the battery fell below 1.000 volt .The capacity was found to be equal at  1.92 Amp.Hours with a final voltage down to 1.000 volt .It should be noted that the capacity is only 1.28 amp.hour if the final voltage is 1.100 volts .The final resistance of the battery at the end of the discharge (R=Delta U/Delta I) was found to be equal to   6.2 Ohm .

Full size diagram

REVIVAL TEST WITH LEKIUM BATTERY

After the complet discharge down to 1.0 volt the lekium battery  was use in a serie of charge/discharge test at various rates as shown hereunder  .The  charge was done either at 40 mA or at 100 mA during various durations from  6 to 28 hours and the discharge until the voltage reach 1.100 volt acroos the battery .The amount of energy fed to the battery was calculated (Amp.Hour) and also the energy recovered during the discharge .A total of  19 cycles were done according to this scheme (First 11 cycles current   fist eleven cycle Voltage  ) .As it can be seen and calculated the yield expressed as the ratio in % between the eneregy recovered and the energy fed     fluctuate in the 40-50% range    .The resistance of the battery does not change that much during the cycle keeping a constant value in the 5 to 7 ohm range .During these 11 cycles the battery was able to give back a total of  2.6 amp.hour , almost twice as much as it gives when just bought .

Cycle number	milli Amp charging current	amp.Hour fed	amp.Hour recovered	Yield
1 2 3 4 5 6 7 8 9 10 11	40 40 40 40 40 40 40 40 80 80 80	0.68 0.44 0.24 0.27 0.32 0.192 0.68 1.12 0.41 0.56 0.79	0.108 0.278 0.195 0.28 0.26 0.1 0.284 0.416 0.24 0.086 0.35	16% 63% 81% 100% 81% 52% 41% 37% 58% 15% 44%

A set of 8 more cycles were done using a constant current of 100 mAmp for charging during 6 hours (0.6 amp.hour charge)  followed by a discharge cycle down to 1.100 volt at 32 mA average   (See the cycle for Intensity   see the voltage. )The yield is fairly constant around  40% .No sign of decline were recorded , the voltage at the end of the charge (with no current ) is constant around 1.45 volt , the resistance of the battery at the end of discharge being also constant in the 5 to 6 ohm region .Te maximum capactity was found equal to 0.41 amp.hour

RESURECTION OF A DEAD "ENERGIZER" BATTERY

A dead battery (ENERGIZER brand)of unknow history (found in a garbage basket ) was subject  to a 17 cycles  trial  as described above.Before charging the voltage measured with no load was 1.23 volt  .Charging was done at 40 mA and discharge down to 1.100 volt  at 32 mA  See Intensity s time  see voltage vs time  .The yield (discharge/charge in %)  was found equal to 38 % on the average .The amount of charge of the battery was limited to  240 mA.h  .At this stage of charge the maximum capacity (amount of Amp.hour recovered at the discharge ) was found to be around 0.2 amp.hour at the beginning  and only 0.1 Amp.hour  at the end of the 17 ieth cycle The resistance of this brandt of battery was in the 3.5 ohm range almost constant during the cycles  .

DURACELL ULTRA M3  RESURECTION

This battery was recovered in the battery  garbage can of  a local department store .The voltage measured was only 0.25 volt , having a normal physical aspect without any leak visible .The battery was subject to a serie of charge/discharge cycle as indicated above (Charging at 40 mA , discharge down to 1.10 volt.at avearge rate of 32 mA  (see Intensity vs time)  (see voltage vs time)

Cycle number	charging current (mA)	Amp.Hour  fed	Amp.Hour recovered	Yiield (%)
1 2 3 4 5 6 7	40 40 40 40 40 40 40	0.228 1.11 0.46 0.33 0.36 0.36 0.36	0.03 0.37 0.13 0.17 0.17 0.13	13% 33% 28% 51% 47% 36% kept as is to study leaking current

The yield  is also in the 37% range .The maximum capacity obtained  was 0.37 amp.H .The resistance of the battery at the end of the cycle was found at 5 ohm .After charging the battery was kept as is to evaluate the leaking current over an extended period of time at room temperature .

TEST OF A Ni/Cd BATTERY

This real battery was bought in a department store(Carrefour) .It's type is AAA having a rated capacity of 250 mA.H .It is supposed to be almost perfectly reversible at least during  more than a few hundred of cycles .The starting point was  a completly charged battery  .The discharge was done  at 33 mA current  until the voltage fell below 1.000 volt It was followed by a cycle of charge and discharge as shown herewith  (see full size current)   (see full size voltage diagram)

Cycle number

charging current

Amp.Hour fed

Amp.Hour recovered

Yield

1 2 3 4

unknown 100mA 40mA 40mA

unknown 0.417 0.244 0.245

0.253 0.250 0.252 kept charged

unknown 60% 100%

The rated capactity  is very close to the experimental value .Overcharging the battery cannot increase it