K2 Battery Life

While there may be some folks with actual problems, most of what I'm reading here sounds more like their battery use is fine.

Just to remind folks - here's what the actual K2 advertising, FAQs, etc. say

"Read on a single charge for up to 4 days with wireless on. Turn wireless off and read for up to two weeks."

Click to expand...

Note the language is "up to" and not "at least", "almost" or just plain "4 days" or "two weeks."

They are saying that is the Max you might expect. Not the average, mode, median, etc. The Maximum.

Frankly the battery discharge (assuming the battery is fine, wireless off and indexing all up to date - and you're just using it to READ - not play the minesweeper game or listen to audio, etc.) - will depend primarily on how often you change the page - i.e., how quickly you read and how long you are reading for.

Amazon has no way of knowing how quickly you read and how much you are reading each day (thus actual charge usage) - so how much less than two weeks it is for you would be something very different individual to individual.

When I see folks talking about days or almost week before recharging under what is statistically heavy use* that is actually doing well. I can't think of ANY electronics I have that get than kind of use without a re-charge.

* I suspect that reaching that two week maximum would rely on what the "Average American" reads and most studies I've seen over the years put that well below an hour a day on average.

My DB's father is an RC car fanatic and he has discussed Lipo use and care with the both of us repeatedly.

First off, Lipo batteries work MUCH better when they are warm and cozy.  Battery life shortens significantly when they are cold...so don't leave your Kindle in the car in the dead of winter.

To maintain the life of a a lithium-polymer battery, you should never let the charge go below 80% discharged (20% battery life remaining).  Letting it go below 80% discharge will lower the number of times you can recharge your battery.  Also, be sure you are using the charging cord specific for the Kindle. A SLOW 1c charge is really the maximum rate of charge, otherwise you risk damaging the battery or causing it to ignite.

Speaking of damaging the battery...I don't want to cause anyone undue fear or paranoia, but people should be aware that they need to take special care not to damage their K2 (and be aware to heavily monitor their K2 if they do somehow have an accident). 

I'm sure that Amazon has taken special care to help insulate the battery, but Lipo batteries are notoriously fragile and can catch on fire if the battery guts are exposed to air.  If you have dropped your Kindle rather harshly, you might want to baby-sit it for a while and not leave it laying about in an area of the home succeptible to fire.  Also, DO NOT charge your K2 without monitoring it until you're able to determine whether the battery has been damaged, as damaged batteries can ignite rather suddenly.  So to be on the safe side, for a time don't set your K2 to charge while you are sleeping...better to watch it charge while you are at your desk at work and can feel your K2's temperature from time to time...any significant warm-up indicates a damage battery and should be immediately removed from the charging source.

I guess that's it.  Sorry if this scares anyone, but it's better to be safe than sorry.

Gary Edward said:

The Kindle battery indicator may also acquire "digital memory" from not completely recycling the battery.

For Li-Ion/ Li-Poly it is recommended that every 30 partial recharges, you let the battery discharge completely - that is, until the Kindle indicates the battery power is too low (see page 25 of user guide).

This should prevent the battery indicator from giving you false readings of the "various states of the battery".

Click to expand...

Gary, that's not "completely" -- but what they say is not to let it go below half-way without recharging it.

Letting it go to 1/4th full is sort of pushing it. It's not like the old nickel cadmium or whatever batteries.

I plug mine in nightly for 7 months now, with daily reading about 1.5 hours and sometimes I let it go to half-way when I'm very busily doing whispernet along with scads of page-turns, which really drains the battery along with the broadband usage thing and also is not great on the memory as the web pages can be so hard on mobiles. But I read an hour on whispernet the other day constantly downloading pages,
and my battery indicator didn't move. It's going strong.

I think you're right that going down to 1/4th infrequently is okay (but don't do wireless on that).

I haven't read in the many articles lately that you have to clear its battery 'memory' the way you did the old batteries so that it could know how much it actually has. But I have read (just today too) that
letting it run down can actually weaken that kind of battery (and the freezes tend to be from people
who do use them that way).

artsandhistoryfan said:

I haven't read in the many articles lately that you have to clear its battery 'memory' the way you did the old batteries so that it could know how much it actually has.

Click to expand...

Hi ahf.

I think you misread; I was talking about the battery indicator, that is why this type of memory effect is called digital.

Here's a clip from an article by Isidor Buchmann of Batteryuniversity.com:

"Although lithium-ion is memory-free in terms of performance deterioration, batteries with fuel gauges exhibit what engineers refer to as "digital memory". Here is the reason: Short discharges with subsequent recharges do not provide the periodic calibration needed to synchronize the fuel gauge with the battery's state-of-charge. A deliberate full discharge and recharge every 30 charges corrects this problem. Letting the battery run down to the cut-off point in the equipment will do this. If ignored, the fuel gauge will become increasingly less accurate."

Read the full article here:

http://batteryuniversity.com/parttwo-34.htm

Additional info:

http://www.batteryeducation.com/2008/08/digital-memory.html

-Gary

Hi again,

Gary Edward said:

Hi ahf.

You must have misread; I was talking about the battery indicator, that is why this type of memory effect is called digital.

Click to expand...

How could I have misread? We're both talking about the battery indicator, as we have no way otherwise of knowing when it's run down until it just stops working.

Thanks for that article. After 30 short charges is, at the very minimum, once a month if one charges it every night.

..."A deliberate full discharge and recharge every 30 charges corrects this problem. Letting the battery run down to the cut-off point in the equipment will do this."

Click to expand...

But what is a "deliberate FULL discharge" and what is the battery "cut-off point in the equipment" ? When it stops working when we're trying to do something?

There's a danger in citing one article applied to a specific piece of somewhat fragile item like the Kindle for which we have had countless stories of people with constant problems with freezes with their Kindles along with a tendency not to watch the battery at all. The freezes have been most often seen to be due to low-battery conditions at a time when battery-intense activities are going on (trying to access the web to download something).

"If ignored, the fuel gauge will become increasingly less accurate."

I imagine that's why Amazon reps have said in interviews to recharge it when it gets to below 50% on the gauge. They always stress there's no harm by topping off since the charging stops when it's done.

That way you can be more sure of stability with it. Hard to know what will constitute accurate memory when OTHER battery experts (in their work) are on the forums saying that you can really weaken this type of battery by letting it run down; it just doesn't like it while the old type of battery thrived on it.

Another interesting aspect mentioned has been that people shouldn't get backup batteries early on because they run down at about the same rate whether used or not and if you have one sitting in a drawer for a year, unused, it will still have only 50% capacity at the end of the year. For those of us who have used one for 6 months, say, then it's about 75%.

Gary, I didn't think it was fair for me to leave you without any citations at all, so I went looking.

Here's what I found. And the bottom section that I got to last is ultra interesting.

===============
http://www.amazon.com/An-Informal-Survey-Kindle-Problems/forum/FxBVKST06PWP9B/TxYUG938VRTT2O/1?_encoding=UTF8&asin=B000FI73MA
In reply to an earlier post on Mar 4, 2009 4:42 PM PST
Beast says:

Remember that Lithium Ion batteries are a great advance in a powerful very dense/small package - but they have do not behave the same as other batteries.

Pros: Small lightweight high energy density compared to other batteries. No memory

Cons: Each cell must not be discharged below 3 volts per cell or the cells can reverse and damage the battery. So don't let the batteries "fully discharge". The Kindle power circuit and charger should prevent full discharge - but it sounds like from some of the postings - they may be discharging more than acceptable.

Don't treat the Lithium Ion battery like other types, you can recharge when 1/2 wayOlder NiCad batteries could be fully discharged and r

=======

http://www.amazon.com/battery-life-in-kindle-2/forum/FxBVKST06PWP9B/Tx3W47GK64ATDBH/1?_encoding=UTF8&asin=B000FI73MA

In reply to an earlier post on Feb 10, 2009 10:39 AM PST
Nicholas Nitka says:
Here is part of directions from the "About your Kindle" in reference to taking care the "battery".

Tips for Conserving Your Battery
The Kindle battery will have a much longer life if you charge it
frequently, rather than waiting until it is fully drained to charge it.

The battery may need recharging if it has not been used for a long period
of time, whether or not it was fully charged before it was stored.

=======
http://en.wikipedia.org/wiki/Lithium_ion_battery

They are one of the most popular types of battery for portable electronics, with one of the best energy-to-weight ratios, no memory effect, and a slow loss of charge when not in use.
. . .
Li-ion batteries do not suffer from the memory effect. They also have a low self-discharge rate of approximately 5% per month, compared with over 30% per month in common nickel metal hydride batteries (Low self-discharge NiMH batteries have much lower values, around 1.25% per month) and 10% per month in nickel cadmium batteries.

[other information there]
...Furthermore, they may be irreversibly damaged if discharged below a certain voltage. To reduce these risks, li-ion batteries generally contain a small circuit that shuts down the battery when discharged below a certain threshold (typically 3 V) or charged above a certain limit (typically 4.2 V).

=======
http://en.wikipedia.org/wiki/Lithium-polymer

[ No mention of memory effect]
[They give reasons why the battery must be protected from overcharging by limiting the applied voltage.
That should be when our Kindle 1 light goes off
and when the Kindle 2 light turns green.]

During discharge on load, the load has to be removed as soon as
the voltage drops below approximately 3.0 V per cell (used in a
series combination), or else the battery will subsequently no
longer accept a full charge and may experience problems holding
voltage under load.

[ Do they mean from a forced discharge? ]

However, in recent years, manufacturers have been declaring upwards of 500 charge-discharge cycles before the capacity drops to 80%

. . .
Self-discharge rate 5%/month

[Guidelines that include Gary's quote as one that -may- be necessary to
recalibrate the battery's monitoring, though not to save life of battery]

Guidelines for prolonging Li-ion battery life
* Like many rechargeable batteries, lithium-ion batteries should be charged early and often. However, if they are not used for a long time, they should be brought to a charge level of around 40%-60%
* Lithium-ion batteries should not be frequently fully discharged and recharged ("deep-cycled"), but this may be necessary after about every 30th recharge to recalibrate any electronic charge monitor (e.g. a battery meter). This allows the monitoring electronics to more accurately estimate battery charge.[23]
* Li-ion batteries should never be depleted to below their minimum voltage, 2.4 V to 3.0 V per cell.
* Li-ion batteries should be kept cool. Ideally they are stored in a refrigerator. Aging will take its toll much faster at high temperatures. The high temperatures found in cars cause lithium-ion batteries to degrade rapidly.
* Li-ion batteries should not be frozen [40] (most lithium-ion battery electrolytes freeze at approximately -40 °C; however, this is much colder than the lowest temperature reached by household freezers).
* Li-ion batteries should be bought only when needed, because the aging process begins as soon as the battery is manufactured.[23]
* When using a notebook computer running from fixed line power over extended periods, the battery should be removed,[41] and stored in a cool place so that it is not affected by the heat produced by the computer.

[The 'Safety' section is an interesting read. Luckily our Kindles don't heat up
the battery the way cellphones and laptops do (remember the Dell laptop fires with the
Sony battery of this type?) I'd keep it out of direct sunlight for prolonged periods
though when in an enclosure like a car with shut windows.

=======
The site that that Gary used (or one similar to it)
http://batteryuniversity.com/partone-5.htm

+++++
Lithium-ion
There is no memory and no scheduled cycling is required to prolong the battery's life. In addition, the self-discharge is less than half compared to nickel-cadmium, making lithium-ion well suited for modern fuel gauge applications. lithium-ion cells cause little harm when disposed.
. . .

Aging is a concern with most lithium-ion batteries and many manufacturers remain silent about this issue. Some capacity deterioration is noticeable after one year, whether the battery is in use or not. The battery frequently fails after two or three years.
. . .

# Low Maintenance - no periodic discharge is needed; there is no memory.

+++++
The lithium Polymer battery [Customer reps refer to it as lithium ion for some reason -it's likely a combo.]

No improvements in capacity gains are achieved - in fact, the capacity is slightly less than that of the standard lithium-ion battery. Lithium-ion-polymer finds its market niche in wafer-thin geometries, such as batteries for credit cards and other such applications.

=====================================================

FROM CUSTOMER SERVICE SECTION OF AMAZON FORUM FOR KINDLE2
http://tinyurl.com/kindle-2-forum

" Posted on Mar 2, 2009 6:01 PM PST
Amazon Kindle Customer Service says:
Good Evening. This is the Official Amazon.com Customer Service post for 3/02/2009

Charging your Kindle battery
With Kindle 2's battery you don't need to fully drain the battery before recharging, or wait until the battery is fully charged to start using it again. The Lithium-ion battery is optimized in such a way that incomplete charging won't affect the battery life. For example, if you drain the battery halfway two days in a row while fully charging both times at night, this would only count as one charge cycle. Leaving Kindle in extreme temperatures, like in your car, will have the most negative impact on the overall life of your battery.

Leaving wireless turned on or sustained use of the wireless functions will cause the battery to drain faster. If you would like to turn the wireless off, select menu from the home screen. Use the five-way controller to select "Wireless Off". Also, downloading a large number of books at once will cause the device to index new content. If you have recently transferred or downloaded a large number of books it is recommended that you leave the device turned on and connected to the charger overnight.

As with any other aspect of Kindle, if you think that your device is not performing as it should, please have detailed notes of your usage and the battery life experienced and contact customer support:

https://www.amazon.com/gp/help/contact-us/kindle-help.html

=======

OTHER ***VERY INTERESTING*** things from Customer Service's official Thread in Kindle 2 forum
http://tinyurl.com/kindle-2-forum

3/4/2009 posting:

"Last Page Read
You do not need to power down Kindle 2 between reading sessions, it is best to leave the device in sleep mode. Holding the switch at the top to power the device off is similar to pulling the power cord on your computer without shutting down the Operating System. If you turn the device off while in the middle of the book, the device cannot save that location. We save the location when the device goes into sleep mode or when you leave the book, so if you do need to power the device off then be sure to go to the Home screen first - this will save your last place in the book.

Wireless Signal in Sleep Mode
Kindle's wireless signal uses low power while in sleep mode so that your subscriptions can download overnight. If you are in a low coverage area, this could cause the device to use more battery power as it continually tries to maintain a signal. Unless you are subscribed to periodicals that you want to receive overnight, we recommend turning wireless off (Press the Menu button and select "Turn Wireless Off" of the menu options) before leaving the device in sleep mode. This will further conserve battery power.

================================================================

Gary, while letting it run down after 30 charges or so may help the battery monitoring,
I think Amazon may be more worried about the effects of letting it run down and not
being able to control how much this might be done. Users let them run down without
even knowing it.

WORSE, mine defaulted to Wireless ON when I opened my unit. That means that
if I didn't know how to turn it Off because I had not read the manual yet, it would
be draining away and that seems to be true for many on the forums who are
wondering why their battery life is so short and wondering where to turn wireless off