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Engineering Corner #1
Battery Myths
By Danny Rockett, GTS Vice President of Manufacturing and Technology
We have all heard the following statements from a variety of customers, purchasing agents,
end users, and associates:
“I buy the OEM (or substitute „major brand name‟ manufacturer) for all my battery
needs…their products perform much better and last longer.”
Or, “I like this product the best since you cannot trust the generic brands; they just don‟t have
the power.”
Another scenario: “I must recharge my battery device each night to get the best
performance.”
And to the other extreme: „”I let my battery product discharge down completely until it shuts
off….this eliminates the memory issues…You know these batteries have memory, my great
uncle told me so many years ago.”
Are any of these true? Maybe, maybe not. As with anything, the background conditions must
be clarified before a true answer can be given instead of relying on a myth from a wise uncle.
Let‟s investigate several old wives‟ tales regarding battery usage. The following myths are
based on lithium battery chemistry including cylindrical, prismatic and lithium polymer cells,
since these are GTS‟s prominent product lines.
False: Highest battery rating wins
My battery is rated higher than yours, I win! WRONG. Two battery packs with exactly the
same rating under the same test regimen will perform differently from one another. That‟s a
fact. This is due to internal impedance of the cells, the charge level dictated by the internal
electronics, and the characteristics of the cell design. The true available and usable capacity
can only be verified in the intended application for which the battery was designed. The two
packs can be tested under the same charge and discharge regimen (using a Cadex or other
battery test equipment) to measure deliverable capacity. But remember, performance in the
application can and will be different for two battery packs with the same rating assembled by
two different manufacturers. The rating is nothing more than a fictitious variable yard stick
indicating general information
False: My Lithium battery has built-in memory
Lithium chemistry has no memory effect within its performance cycle. There is no false
capacity step within the discharge process that prevents the battery from discharging further.
It does not matter if the battery discharge regimen was continuous, sporadic, or to varying
depths. With lithium chemistry, capacity out of the product is not limited by any internal
chemical process (unlike the well-known memory issues with nickel chemistry).
False: Quick charging battery packs reduce their cycle life
Within reason and always per manufacturer‟s specifications, slow, quick or fast charging of
lithium cells will not damage or decrease overall cycle life of the product. Only the total
amount of usage (full charge and discharge cycles over time) reduces the battery‟s life (in
conjunction with the environment temperature, depth of discharge, impedance growth and
other factors).
False: I should top off my battery before usage
Obviously, if a pack has been in storage for some length of time, then a topping charge may
be required. However, under normal conditions and after short storage periods of days to
weeks (this also includes short lack-of-use periods), a topping charge is not required. Lithium
battery packs have a very low self-discharge rate, which means the chemical decomposition
reactions inside the cell are minimal. Self-discharge at room temperature is only 2% per
month. And there is a small amount of current flowing due to the internal safety and fuel
circuitry. Even with these two combined energy losses within the battery pack over time, in
most instances, if the pack was fully charged previously there is no need for a topping charge
after a brief lack of use.
True and False: I should remove my battery pack from the charger to conserve life (and
of course energy)
We hear this all the time from many associates: “Remove the pack from the charger, it saves
the battery.” From the standpoint of conserving battery cycle life, this is False. All Li
chemistry chargers terminate the charge voltage and current at the appropriate time, so
therefore no energy is flowing into the battery pack. The charger must cycle back on (due to
decay in battery voltage from self-discharge or current draw of electronics) before energy
again flows into the battery pack. The battery pack is not being charged due to termination
and therefore cycle life is unaffected.
True from the standpoint that the charger is sitting idle even though the battery current and
voltage flow has terminated. The charger power supply is consuming some amount of power
from the AC voltage line during this idle period. With high efficiency power supplies, this
power consumption is small. A large operation with many power supplies and chargers may
benefit from a complete shutdown of the chargers but this is difficult to manage and to keep
batteries fully charged for the application.
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So, bottom line for industrial applications: leave the charger plugged into the wall, leave the
battery in the charger. There is no detrimental effect to the pack or the charger.
False: I must charge my Lithium battery fully for 24 hrs before I can use it the first time
Lithium battery packs do not require any long-term charging for first use. After a normal
charge (per manufacturer‟s recommendations), the product is ready for use. Remember,
most lithium-based products are shipped with <35% residual charge level to eliminate any
problems with non-recoverable capacity. So, your initial charge will bring the product from
the residual „shipping” charge level to full charge without any first time „long‟ charge
regimen. One exception that we know about is with Impres™ chargers and battery packs for
two-way applications. During the first 24 hour period, the charger does balance and
condition the cells within the OEM packs. However, this is not the case for 99% of all other
applications, chargers and battery packs.
False: I have to recondition my battery packs to restore life and improve performance
Lithium-based chemistries do not require reconditioning. Since there is no inherent memory
problem, reconditioning does not improve performance nor does it restore life. Actually,
reconditioning will remove one cycle from your overall battery life each time it is performed
so it is a waste of time and energy to perform this procedure.
Reconditioning is recommended for some lithium batteries to reset and recalibrate the
internal fuel gauge electronics. During use, the fuel gauge can become inaccurate due to the
electronics‟ method of tracking energy into and out of the battery pack, impedance growth,
etc. Because of this, the fuel gauge may indicate greater or lesser amounts of capacity than
the battery can actually deliver. All of the newer impedance-track fuel gauge technology in
use today does not require conditioning.
False: Avoid charging the battery unless it’s fully drained
Waiting for the battery to be fully drained of energy before recharge does nothing to improve
performance, regain any lost capacity, conserve life or reduce the cost of the next recharge.
Lithium batteries can be charged at any time without any negative effects. There is no need
to wait until the battery is flat to charge it back up to full capacity.
True and False: Let the battery drain completely a few times a week
False from the standpoint of draining the battery completely. Unless you are performing a
recalibration or conditioning procedure (for the purpose of resetting the fuel gauge), there is
no need to routinely drain the battery completely.
True from the standpoint of allowing a small discharge and charge routine during a storage
period. This, of course, does not need to be several times a week, but maybe once every
week or two. Lithium batteries like to be exercised. A little exercise is good for the inner
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electrode structure and avoids any storage at 100% residual charge levels (remember again,
non-recoverable capacity losses).
True and False: Date codes indicate condition of a battery pack
The date code of a battery indicates when the battery pack was manufactured. It is also used
for tracking a particular production lot if there are subsequent quality issues and to indicate
the beginning or ending of the warranty period.
Battery date codes MAY advise whether the battery is old and should be replaced. However,
if the battery pack is performing the needs of the customer, then there is no need to remove
it from service just because it is X number of months or years old. Similar date codes for two
identical packs are not an indicator that both packs are good or bad; it all depends on their
usage pattern during the period since manufacture.
True: Overcharge is bad for Li-ion
Overcharge for any battery chemistry is bad. However, lithium batteries have internal safety
circuits to monitor charge input and voltage levels. As these levels are reached, internal
components will switch the battery pack off, avoiding damaging overcharge levels. Using
correctly-designed and -built lithium chargers, their electronics have preset limits on
charging, preventing overcharge conditions. So, if all systems are working properly, a user
cannot overcharge a lithium battery pack, due to the redundant safety features built into
every lithium battery and charger.
True and False: Depth of discharge affects cycle life
Cycle life is dependent on many items: impedance growth of the cells, storage conditions,
charge conditions and levels, and environmental temperatures. These are the largest factors.
As lithium batteries are cycled with short or shallow charges and discharges, cycle life is
better over the long haul. However, the converse may or may not be true. Under some
conditions, cycle life could be just as good if the product has been cycled with full versus
partial discharges. As my friend Bill Godsey at Sanyo once said: “It depends on the usage
conditions!”
Summary
As you can see, there are many myths concerning lithium chemistries and the battery packs
containing these cells. Since GTS is the technical leader in applications, product
development, battery assembly and testing, customer support begins with debunking the
many myths that continue to be passed along from the untrained battery person. The next
time you hear one of these myths being discussed, you are now better informed to set the
record straight.
Until next time, stay charged!
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