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laptop batteries - too smart ?

Posted on 2013-02-05
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Last Modified: 2013-02-18
hello,

i have had recently to replace 2 batteries for HP Pavilion laptops.
Since i enjoy learning and testing, i opened the battery packs for inspection.
one has the 18650 -2200mAh type cell of 3.7V; the other is more powerful.
Anyway; i was able to charge both battery assemblies, and tested they deliver up to 3 A, which should be enough for booting.
This brings me to my question :
Since the Batteries seem ok -  it looks like the failure to boot up is due to the smart battery circuitry in each pack.
i do not believe both sircuits failed, but it is possible.
does anybody out there have the same experience ?
Or Is HP building a SMART circuit into the pack that  disables the loading - or use of the pack?

very curious to see the reactions
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Question by:nobus
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by:Ben Hart
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Wow that is neat but not too surprising.  I have always been under the impression that the circuits inside a battery pack would provide info like cell life, drain rate, charge rates, authentic (HP,Dell,IBM,etc) battery info.

are you in a position to try a generic battery?
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by:rindi
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Modern batteries can explode if they get too hot. The circuitry probably checks for that and if certain thresholds are reached it marks them as unsafe.
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by:nobus
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li-ion batteries don't get hot, afaik - but i maybe wrong.
i know there is checking circuitry i nvolved, but i'm curious if it's the same play again like with the printer cartridges, some time ago, stating it must be replaced, while they still can print...


i'm hoping to get some personal experience here
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by:_
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I don't do many laptops, but I have seen batteries that measure OK with the meter, but tank as soon as a load is applied (you can watch the meter drop like a stone).

Doesn't answer the circuit question, but something you might check.
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by:nobus
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i thought about that Coral, and loaded it upto 3 A and more
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by:tliotta
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li-ion batteries don't get hot, afaik - but i maybe wrong.

Generally true, as long as they are well manufactured with no, or very minimal, metallic flake impurities and no short circuits cut across the cell separators.

But otherwise, they can get very hot, explode or melt.

Tom
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>> ...loaded it upto 3 A and more

Okey doke. I will go sit over there and see if I can learn something new, then.  ; )
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The circuit inside the battery serves two purposes. One it monitors the battery temperature during charging and sends a signal to the micro controller based main charging system inside the Laptop to shut down the charging process. Secondly it has an in built over load protector which protects the battery from dead shorts. This is because to protect the user too as the battery will be usually a Li ion which can deliver more amperes that expected which may play havoc during any mishap.
Some people say that a Li-Ion battery kept at full charge loses about 12-15% of its rated mAh capability each year. If kept at 50% charge it loses much less, about 4% each year.

Some interesting links about rebuilding the battery pack, the circuit inside, the firmware and the protocol of communication SBS:

http://www.linuxjournal.com/content/rebuilding-laptop-battery
http://batteryuniversity.com/learn/article/how_to_repair_a_laptop_battery
http://mods-n-hacks.wonderhowto.com/how-to/hack-dead-laptop-battery-250860/

http://www.electronics-lab.com/articles/Li_Ion_reconstruct/
http://frantisek.rysanek.sweb.cz/battery.html#downloads
http://www.zdnet.com/inside-a-notebook-battery-pack-3039281143/
http://www.sbs-forum.org/
http://computer.howstuffworks.com/dell-battery-fire.htm
http://laptop-batteries.over-blog.com/article-what-s-inside-a-laptop-battery-pack--42533170.html
http://www.youtube.com/watch?v=j4DlUUZxFvs
http://www.tomsguide.com/us/how-notebook-batteries-work-and-why-they-blow-up,review-838-7.html

http://media.blackhat.com/bh-us-11/Miller/BH_US_11_Miller_Battery_Firmware_Public_WP.pdf
http://www.g-batteryshop.com/blogs/How-to-service-laptop-batteries.htm
http://sbs-forum.org/specs/sbdat110.pdf
http://batteryuniversity.com/learn/article/inner_workings_of_a_smart_battery
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by:nobus
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what are you trying to say Viki?
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by:viki2000
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if you look over the links then:
- some will show that the laptop battery can catch fire in some situations
- the links provide information about the smart circuit topology inside the battery pack, including the protocol of communication SBS
-if you want to find a clear answer to your question then you need to make some tests. Those tests implies knowledge of the circuit design, firmware and SBS protocol, in case you are ready and able to analyze that
-take for example only next link http://media.blackhat.com/bh-us-11/Miller/BH_US_11_Miller_Battery_Firmware_Public_WP.pdf . You have to do something similar. When you are able to connect on SBS bus and intercept the communication between battery and laptop then you will know for sure what is going on.
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by:nobus
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awful lot of info - thanks far that anyway; i was not sure if you wanted to stress something, so tx for the update

can someone answer one of these :
-if a batterypack is declared dead by the smart circuitry -  can it be revived (the circuitry status)?
-what is the best method to check the batteries themselves, other than charging/unloading them?
-are the battery circuits the same for each supplier?  or are they different for different brands?
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by:viki2000
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I can answer some of that because few months/years ago I tried to find out by myself if something can be done home for the laptop battery. I ended in buying new cheap battery from China and they are good enough for the price that I paid.

The circuit inside is not the same, depends by IC circuit used for battery management. I can give you 10 links minimum with different kind of such circuits. In their data-sheet there is sometimes a general schematic. So first step is to identify correctly the IC inside the battery pack.
The only thing similar is the SBS protocol, but not the sequence of communication with the laptop.
It is not easy if you cannot connect to SBS bus and have access to the circuit signals.
Some of them use small micro controllers instead of dedicated ICs, then is harder.

The best method to find if the cells are still good is only to use an external charger/discharger, battery tester.

I know that I have read about it, but I am not so sure now- as I have so many info in my head daily, but regarding your first question:

- there are links on the net which show even with picture how to replace the cells and use the same old circuit - if you need I can search them
- now, if I remember well - but I am not so sure, some of the circuits have a kind of memory and even if you replace the cells, the circuit does not recognize that - similar with printer cartridges refill - and then you need a kind of reset. I have read even about such procedure - but was no universal - in order to bring everything back to normal.

The question remains: how do you know that the circuit has no problem before you try anything else?
The circuit inside the laptop is easy to be tested with another battery, but the circuit inside the battery after cells replacement with new - I do not know now another method except the SBS protocol analysis.
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by:viki2000
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And related with the last link that I gave you (Miller guy with firmware) - if you can do such things, then you control the battery and you are "master" of battery as these guys:
http://www.pcworld.com/article/236875/batteries_go_boom.html
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by:nobus
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still reading thru all the stuff..
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by:nobus
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i suppose i got enough info for now
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by:viki2000
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Thank you for points and good luck by swimming in that ocean of info. I personally renounced when I found it, because the matter of battery was not related with any business, was only  a private one and made no sense for me to spend time and dig so much in order to be a "master" of batteries.
I wish you success!
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by:nobus
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if i persue the matter, and have results, it will be thanks to you
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