Kindle 3 Battery Usage and Charging

Basics about the Amazon Kindle 3 battery and how to charge it.

Out of  the box, the Kindle is equipped with two  ways of charging – one the supplied charger, the other is to use your computers  USB port as the charger.    The USB port on the Kindle is one of the newer miniature narrower types (micro B),  standard on many cell phones and blue-tooth devices.   Both of these methods work great.  I  don’t recommend trying any other charges unless for some reason, circumstances force you to take a chance on a third party charger.

The Kindle 3 Battery

The Kindle 3 has a 3.7 volt, 1750 mah Lithium Polymer battery for a fairly hefty battery capacity.  The battery is made in China,  which manufactures much of the industrial worlds batteries. The battery is likely to be a fairly generic unit selected for size and capacity.   Charging techniques are well established for LiPo battery chemistries and is basically the same as for Lithium Ion.  The key is control of the current used in charging, and to monitor and control the voltage applied to the battery.   A typical charge curve for a generic 3.6 V LiPoly device employs an initial  850-900 mah constant current charge (CC) for the main charge phase until the voltage climbs to a maximum 4.2V, followed by regulated constant voltage of 4.2V (CV) while  the charge  current drops to approaching zero.  Deviating from this strict regime invites the  destruction of the battery.  All consumer charging circuits are designed to protect the battery while charging it.  By convention, LiPo batteries can be charged at a maximum charge current of 1C (where C is the capacity of the battery) and most commercial chargers provided by the manufacturer  provide less than this 1C charge which, for a 1750 mah battery,  would be 1.7A (amps).    However, if you want the battery to have a long life,  the charge rate should  be less than 1C

The Kindle 3 comes with a  compact 4.9v 850ma charger with a  USB socket for the charge cord that doubles as the USB link to the computer and enables  the Kindle to charge while attached to a  computer USB port.    The computer’s USB 2 port supplies 500 ma,  a lower charge rate than the included charger. Higher charge currents charge faster, so expect the wall charge to charge faster.  850 ma is about 0.5c  rate for the battery so  a full charge is mathematically about 2 hours,  but because of the charge algorithm, charging will take longer for a full charge.   When the battery approaches 4.2V a “smart” charger  switches from a constant current to a constant voltage (CV) for the remainder of the charge while the current drops as the battery approaches a full charge.  For the USB port, the calculated full charge time is more like 3.5 hours, again with a large fudge factor.

I don’t think I’ve ever charged my Kindle as long as 2 hours using any charger.  That’s probably because I don’t let the battery level drop too low.  It’s best to top off the charge whenever you get the chance with Li rechargeables and never let the charge get to the point that the device cuts off the power.

The charge circuit is built into the Kindle.  It is possible the charger is relatively “dumb” (I don’t know and haven’t tried to test it), but the job of even a dumb charger is to  stop the charge as the charging voltage reaches 4.1V.    If the charger did not follow up with a constant voltage charge at 4.1 v, the result  would be a reduction in run-time, but a likely gain in overall battery life, which is fine for me since the run times are already some of the longest you’d see in an e-reader. Otherwise the charge goes on longer and the run time approaches the maximum possible.  Either way works for me but a smart CC/CV charger shows a better engineering effort.  Hopefully I’ll find out what the deal is with the Kindle and get a chance to update this info.

How about using a cell phone (or other device) charger?

While I don’t recommend it,  there are situations where this would be convenient.  I’ve read several posts on the web of people who have used cell phone chargers on the Kindle with no issues.  The problem is that there is a very wide variety of chargers out there, some of which may be incompatible with the Kindle.  Here is some information that I hope reduces the risk to your Kindle if you.  Beware, unless you know the charger and what it is designed for, it is not possible to know what will work and what won’t with 100% certainty.  It’s your call!

Make sure the output voltage is  4.9-5.0v DC  (the voltage “V” will be stamped on the charger).   I don’t know whether the Kindle can handle outputs above 5.0V at this time, so I would avoid higher voltages as unknown and possibly unsafe.  If anyone has tried it let me know.   It is safest to use chargers that are designed for miniature LiPo/Li-Ion batteries in personal electronic devices.  These have the best chance of sharing the same level of technology with the Kindle.  The USB plug must fit.    Most cell phones use with lower capacities than the Kindles so using those chargers should be OK  unless the charger has a higher voltage than 5v or a charge rate exceeding 1750 ma at the extreme end.   Something between 500 ma and 850 ma is optimal.   Most of the time,  the current supplied by the charger to be lower than the Kindles charger,  resulting in a longer charge time.  This is because most cell phone batteries are not as beefy as the Kindle’s as far as total capacity.

More comments on generic, after market chargers, or a charger you have laying around the house. Assume that using any third party charger  not recommended by Amazon will void your warranty.  Common brick chargers  used for cell phones rated at 4.9V – 5.0V and 500 MA or less are probably safe.  Don’ts: If the rating exceeds 1750 ma (or 1.7 amps), don’t use the charger.  Any  charger that puts out AC and not DC is definitely incompatible – this is rare but not impossible with very specialized chargers.  Don’t use chargers designed for printers, dust busters, phones or anything but miniature Li-Ion/Li-Poly devices manufactured recently.   A hobby charger, a specialized charger, or a “smart” charger may be incompatible with the Kindle.  Don’t use these specialized chargers.    If you don’t know what a charger was designed for, don’t use it.

A few charging guidelines.  This would apply to all chargers including the OEM Kindle charger. As always, let common sense and temperatures be the guide in charging electronics.  If the device  ever feels hot while charging,  stop.  Hot is seldom a good thing (unless you race RC cars, in which case safety, economy, and all else is sacrificed for speed).  120F degrees  for anything but RC car batteries is  hot.   Warm… well charging is a warm activity. My Kindle on it’s original factory charger seems to charge without getting warm except possibly at the very end of the charge when the light turns from amber to  green.  The brick itself is warm throughout the charge and cools toward the end.

Run times.   Naturally, the longer the better for convenience.  Some things that affect run time include the following:

  • listening to music (reduces run time to a few hours – too bad…)
  • wifi/network turned on
  • indexing new books (internal processing that occurs soon after downloading new books)
  • turning pages

Most rechargeable devices  batteries will survive more charging cycles if they are never fully depleted and never fully charged to their rated capacity.

Some internet research brings up a few factoids regarding the internal components of the Kindle 3.

- 3.7V, 1750mAh (6.5Wh) Li-ion battery . Type number 170-1032-00 model number GP-S10-346392-0100

- AnyDATA DTP-600W HSPA mini PCI-E module
– Freescale ARM 11-based i.MX353 multimedia applications processor. Part number: MCIMX353DJQ5C
– Samsung K4X2G323PB-8GC3 DRAM
– Samsung 4GB moviNand storage chip — KLM4G1DEHM-B101
– EPSON KCRE7000 F10203TYV E-Ink display controller
– Atheros AR6102 ROCm WLAN chip (AR6102G-BM20)
– Wolfson Microelectronics WM8960G stereo codec

Refences:

Disclaimer.

When it comes to  using the information found here and especially trying out third party chargers, please understand that the reader  assumes all risk and liability.

 

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12 Responses to “Kindle 3 Battery Usage and Charging”

  1. Hi
    I own K3 3G and I stay in India
    I own a third-party AC power adaptor(Philips) with following specifications:
    Input 100v-240v
    50/60hz
    0.15 A
    output: 5.4 – 500mA
    Can i use the above adaptor to charge my Kindle

    • marksun Says:

      Hi sorry it took sooooooo long to get back to you. It think it would “probably” work if your adapter is designed for charging “generic” devices with LiIon batteries using the usb jack, and the few other conservative warning signs I mentioned. But there is tolerance for voltage, especially low voltage DC in most devices. If I was to try it on my own Kindle, I would look at the charging light for normal operation, then watch the temperature of the charger and the temperature of the kindle. If it anything ever felt more than warm, I would stop.

  2. Thanks, perfect explanation. I’m trying to minimise bulk and weight for a cycling holiday and hope to use my Nokia charger (output 5.0v 800mA) for the kindle, with a 2mm Nokia-to-micro usb adaptor. First attempt, I noticed the Nokia charger getting warm after 5 minutes. Oh no! Unplugged it. Googled. Thanks to internet and your write-up I’m reassured re warm, I’m back up and running, my tests continue! Thanks again.

  3. marksun Says:

    Hi Tom, thanks for the note. Heat is the enemy of all things electronic. As far as the charger is concerned, shorter and more frequent is probably better for it than long charges at full load. Good luck with the testing and have a great trip!

  4. I have a 12v solar system that charges 4 led acid golf cart batteries, and I was wondering about charging the kindle via DC instead of AC. Also, I’ve noticed that there are cigarette lighter adapters for the kindle and I was wondering if these are safe. It appears that there isn’t any safety features in the kindle to prevent over charging. Would you recommend staying away from 12v DC to charge the kindle? Thank you for writing this blog! I assumed the battery was similar to a laptop battery and that it would be good to run down the battery as far as possible before recharging. Thanks to you I learned the opposite was true.

    • marksun Says:

      Thanks for your message! Cool – I always thought there was something magic about solar power. No reason a 12v battery system would not work for stable DC power. You are probably looking for a car charger. How well it works depends entirely on the quality of the charger so that’s where you would want to be sure the spec on the charger is accurate. As for the Kindle, it must have an internal protection circuit to both charge and prevent over charging – that’s standard for devices using lithium batteries (without them, there would be meltdowns!). The 12v (input voltage) charger you use can be relatively simple, just check the specs and polarities (plus to +, negative to -). Labels can be inaccurate so watch the temperature and be wary if your kindle gets “very warm or hot”.

      BTW – most laptops now have Lithium batteries – I keep mine charged and try not run down too far (although often as not I do). With the older NiMh and older still NiCad battery types, running down the battery was the trick thing to do and it benefited battery life, but not with current generation Li.

  5. Kindle Fire Reviews…

    […]Kindle 3 Battery Usage and Charging « Space Time Works[…]…

  6. After reading up a lot on this subject I started to charge my Kindle 3 from my iPhone charger. It’s rated 5V at 1A so I figured it’d be alright as long as the voltage matched. Haven’t had a problem since and it charges much faster (obviously) than from the USB slot on my system. I did worry at first that the Kindle wouldn’t limit current flow into the device and that it would ruin the battery, but it doesn’t seem to get too hot. Your article backs this up too by stating that the current limiting circuitry is on the Kindle itself and not the charger.

  7. WIIL I NEED TO THROW AWAY MY KINDLE 3/4 AFTER ITS BATTERY THAT CAN NOT BE REPLACED GOES DEAD ?

    MARIANO
    luismariano_2000@yahoo.com

    • No need to throw it away. Amazon will replace the battery for a fee. It is also possible to google around a bit and find replacement batteries as well as instructions to do it yourself – not for everyone however.

      As far as how many times can the battery be recharged … there is no single answer because everyone uses their batteries differently and because no two batteries are identical in quality. Like cars, one comes out perfect, the next one off the assembly line is a lemon. On the whole I’d expect the battery to last at least a couple or more years or so, then start to get weaker. Just a guess but I’d think they will last longer than a cell phone battery because the Kindle is a very low power device, far kinder to batteries than a cell phone. I charge my Kindle once a month or so; I read a few hours a week – you know, it varies. This very good battery life is relatively unusual with electronic gagets so, who knows? It’s one of the “pluses” of the Kindle.

  8. Hi. I have used various non-Kindle charges with some success. If the charge level on the Kindle has not fallen too low this works quite well and even a low amperage cell phone charger works fine. But if the Kindle charge level is very low, only a high amperage charger will do, ie higher than 2 or 3 amps output. I have a 12 volt car cigarette lighter charger that will bring the battery back from the dead when all else fails.

    • I have been shutting mine off when I don’t use it. It takes 8 seconds to fully shut off, and during that time I read another sentence or two because 8 seconds can subjectively feel like a minute… and an annoying one at that. But my question here is about the battery and it’s hibernate mode. Is it really efficient? Is it better to shut the Kindle down for the night or simply let the screen saver stay on? Is their some sort of internal CPU that shuts off in hibernate mode?

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