Battery Discharge Test -- "Rest & Rejuvenation"?
After reading the
"Battery Saver Kit" instructions, I wondered if the
"Rest and Rejuvenation" approach really added to the battery life. That is, if the
battery is allowed to rest between uses, will the total "on time" of the radio
be increased? And will longer rests be even better? The battery under consideration is the
Eveready 412, 22.5 volt battery. It is the correct
physical size for the TR-1 and matches the original
specifications for the radio.
I decided to look into this on two fronts. One was to see if there was any existing
research literature to support this. I came across a key paper that addresses this issue:
E.J Podlaha and H.Y. Cheh, "Modeling of Cylindrical Alkaline Cells, Part VI. Variable
Journal of the Electrochemical Society, vol. 141, no. 1, January, 1994,
While this addresses alkaline cells, which are a different
chemistry than that in the Eveready 412, it was believed there
may be some connection. The authors do determine that the rest and rejuvenation
approach has merit, and that it will extend the useful life of the battery.
Portions of the paper are quite technical, employing partial differential equations,
but other parts are very readable.
Battery Discharge Experiments
Next, I decided an experiment was in order. The Regency Battery Saver Kit implies an experiment
of running the radio 2-3 hours per day, using the same battery only every 6th day, or so.
With their estimated battery life under these conditions of around 40 hours, this experiment
could take 20 sessions of 6 days each, or 4 months. While an automated setup could
be constructed to perform the tests, the likelihood that a summer lightning storm
could cause a power outage was significant, and this would render the experiment useless,
requiring it to be restarted.
Instead, two experiments were proposed -- one allowing the battery to discharge without
turning off the radio. This is a harsh operating condition and not likely in practice,
but would yield a boundary condition on the discharge capabilities of the battery.
A fresh Eveready 412 was purchased (from Batteries Plus) and connected to the radio. The battery
terminal voltage was read every minute and recorded automatically. The result
shown here indicates the battery is able to power the
radio for about 19 hours, until the voltage drops below an arbitrary
level of 12 volts. The radio still plays at under 12 volts, but this level yielded
a quiet sound from the speaker, and was chosen as the minimum operating condition
for these tests.
Next, another fresh battery was used in a setup that turned the radio on for just
4 hours per day, allowing it to rest for the remaining 20. The radio's volume
control was set the same as in the first test, and power was applied using this
control apparatus. The power supply
on the left provides power for the digital voltmeter, which is interfaced to the
laptop computer's serial port. Custom software collects the data from the DVM.
The power supply on the right is turned on and off by a standard household
light timer. The supply then turns a relay on and off, making the connection
between the battery and radio. To accomplish this, a piece of paper was inserted
between the battery's "+" terminal and the radio's battery clip. Then a piece of
aluminum foil was inserted between the battery and the paper, providing a contact
to the battery. The result of this experiment
shows that the battery regains some of its voltage during each resting period,
but loses much of that quickly during the next discharge period.
A main question, though, is whether the radio is actually powered longer than
the 19 hours indicated above, before it falls below 12 volts. To investigate this,
only the "on time" of the last experiment is plotted along with the result from
the first experiment. This
comparison shows that the rest and rejuvenation
approach yields about 27 hours of "on time" before dropping below 12 volts --
an increase of 8 hours, or 42% -- certainly significant.
The remaining question is whether a longer rest period would improve the results
even more. The fact that even after 20 hours of rest the battery is still gaining
voltage suggests this possibility. I'll leave this experiment to someone else.
If you have any suggestions (corrections?) or just comments,
please send them along to me, Steve Reyer.
I'd like to hear from you!