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The idea of recharging alkaline batteries is not new. Although
not endorsed by manufacturers, ordinary alkaline batteries
have been recharged in households for many years. Recharging
these batteries is only effective, however, if the cells have
been discharged to less than 50 percent of their total
capacity. The number of recharges depends solely on the depth
of discharge and is limited to a few at best. With each recharge,
less capacity can be reclaimed. There is a cautionary advisory,
however: charging ordinary alkaline batteries may generate
hydrogen gas, which can lead to explosion. It is therefore
not prudent to charge ordinary alkaline unsupervised.
In comparison, the reusable alkaline is designed for repeated
recharge. It too loses charge acceptance with each recharge.
The longevity of the reusable alkaline is a direct function
of the depth of discharge; the deeper the discharge, the fewer
cycles the battery can endure.
Tests performed by Cadex on ‘AA’ reusable alkaline cells
showed a very high capacity reading on the first discharge.
In fact, the energy density was similar to that of a NiMH
battery. When the battery was discharged, then later recharged
using the manufacturer’s charger, the reusable alkaline settled
at 60 percent, a capacity slightly below that of a NiCd.
Repeat cycling in the same manner resulted in a fractional
capacity loss with each cycle. In our tests, the discharge
current was adjusted to 200mA (0.2 C-rate, or one
fifth of the rated capacity); the end-of-discharge threshold
was set to 1V/cell.
An additional limitation of the reusable alkaline system
is its low load current capability of 400mA (lower than 400mA
provides better results). Although adequate for portable AM/FM
radios, CD players, tape players and flashlights, 400mA is
insufficient to power most mobile phones and video cameras.
The reusable alkaline is inexpensive but the cost per cycle
is high when compared to the nickel-based rechargeables. Whereas
the NiCd checks in at $0.04 per cycle based on 1500 cycles,
the reusable alkaline costs $0.50 based on 10 full
discharge cycles. For many applications, this seemingly high
cost is still economical when compared to the non-reusable
alkaline that has a one-time use. If the reusable alkaline
battery is only partially discharged before recharge, an improved
cycle life is possible. At 50 percent depth of discharge,
50 cycles can be expected.
To compare the operating cost between the standard and reusable
alkaline, a study was done on flashlight batteries for hospital
use. The low-intensity care unit using the flashlights
only occasionally achieved measurable savings by employing
the reusable alkaline. The high-intensity unit that used the
flashlights constantly, on the other hand, did not attain
the same result. Deeper discharge and more frequent recharge
reduced their service life and offset any cost advantage over
the standard alkaline battery.
In summary, the standard alkaline offers maximum energy density
whereas the reusable alkaline provides the benefit of allowing
some recharging. The compromise of the reusable alkaline is
loss of charge acceptance after the first recharge.
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Advantages
and Limitations of Reusable Alkaline Batteries
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Advantages
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Inexpensive and readily available — can be used as
a direct replacement of non-rechargeable (primary) cells.
More economical than non-rechargeable – allows several
recharges.
Low self-discharge — can be stored as a standby battery
for up to 10 years.
Environmentally friendly — no toxic metals used, fewer
batteries are discarded, reduces landfill.
Maintenance free — no need for cycling; no memory.
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Limitations
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Limited current handling — suited for light-duty applications
like portable home entertainment, flashlights.
Limited cycle life — for best results, recharge before
the battery gets too low.
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Figure 2-9:
Advantages and limitations of reusable alkaline batteries.
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