# Li-Ion battery from cell phone, why 3 or 4 terminals?



## viorel00 (Jul 20, 2007)

Hi, I have an older Nokia cell phone and the battery has 4 terminals, the outer two are the actual + and _ and the inner one is split in two parts (almost touching each other, no plastic insulation). The cell phone has 4 contacts to the battery.

I have another not-so-old cell phone (Nokia 6030) and I notice the battery has 3 terminals, the outer two are + and - according to the label on the battery, but then there is this middle contact. The phone has 3 clamps (contacts).

So, why this one or two additional contacts on cell phone batteries?

Thanks


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## legtu (Jul 20, 2007)

the extra terminals are usually used for the 'communication' of the battery protection circuit and the phone.


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## TorchBoy (Jul 21, 2007)

They might be labelled + T - for positive, thermistor, and negative. The thermistor is a way for the phone to tell if the battery is getting too hot. I don't know why your first battery would have two almost touching.


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## monkeyboy (Jul 23, 2007)

Cell balancing perhaps?


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## legtu (Jul 23, 2007)

monkeyboy said:


> Cell balancing perhaps?



i haven't encountered a cell phone that uses a battery pack as a power source so it's unlikely that the extra terminals are for cell balancing.


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## ubi21 (Jul 23, 2007)

I'm a little curious too. I got a Nokia N95. The battery has 3 terminals. On the battery label there are 3 circles in this fashion ( O-O-O). The first 2 circles have + and - respectively inside the circle. The last circle has nothing inside (Will now be referred to as O). I decided to use my multimeter on the terminals. I got a voltage reading on the + and -, and + and O. The + and O reading had a slightly lower voltage, by 0.01V, than the + and -. I got a 0V reading when I tested - and O.

Note: I'm not using a fluke meter.


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## Handlobraesing (Jul 23, 2007)

Measure the ohms between O and -. It should change with temperature.


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## sysadmn (Jul 24, 2007)

http://www.edn.com/blog/1470000147/post/240006824.html said:


> So I talked to the battery charging experts at *Maxim/Dallas Semiconductor*. Maxim is one of the major suppliers of battery charging ICs and fuel gauges. They said, yes, the majority – but not all – of cell phones have a thermistor in the battery pack that tells the charger when the temperature is below freezing and prevents the battery pack from charging. They estimated that 80 - 90% of cell phones have this capability. A good way to tell is by looking at the contacts on the battery pack: Two contacts means no temperature sensing capability, a third contact is probably for the thermistor and indicates the charging indeed shuts down at sub-freezing temps. (A fourth contact is probably for a memory device.)


 
Hope this helps!


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## ckthorp (Jul 24, 2007)

legtu said:


> i haven't encountered a cell phone that uses a battery pack as a power source so it's unlikely that the extra terminals are for cell balancing.



The first handset that SprintPCS launched with, the one with the earpiece which slid up-and-down, had a 7.4v LiION pack (with only 2 terminals!).

My bag phone also has a pack, but that's a 6-cell SLA.


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## ubi21 (Jul 25, 2007)

Handlobraesing said:


> Measure the ohms between O and -. It should change with temperature.



Thanks for the info. It is a thermistor.


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## Felim_Doyle (Sep 29, 2013)

TorchBoy said:


> I don't know why your first battery would have two almost touching.


It's an old thread but still very relevant so “wakey wakey”!

I've often wondered about that curious split contact on some older Nokia battery packs. Indeed I have a BLS-2N in my hand right now and it has two such contacts.







The same is also true of some later Nokia slab type batteries such as the BLB-2.






Maybe those contacts are the thermistor(s)!


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## Felim_Doyle (Sep 29, 2013)

Moving to the present, my Samsung Galaxy Ace has a three contact battery (EB494358VU) ...






... but my Samsung Galaxy S4 has a four contact battery (B600BE) ...






... although I couldn't find an image showing the contacts. 

On the B600BE the contacts are marked +U-U where U represents ‘unassigned’ (i.e. unmarked).


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## Felim_Doyle (Sep 30, 2013)

So, if I want to charge a spare battery outside of the phone, do I need to know what the third and, in the case of the B600BE, fourth terminals are for?

I think that we have established that in most quality batteries, there is a thermistor connected between the third, unmarked terminal and the negative terminal. The ‘split’ terminal(s) on some Nokia batteries remains somewhat of a mystery for now.

Is the fourth terminal on the B600BE essential or even critical to the charging process?

I have a generic charger for such types of batteries which only uses the + and - terminals and I'm risking giving it a try on a completely drained B600BE. I'll let you know how I get on!


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## Felim_Doyle (Oct 1, 2013)

Well the B600BE is a 2600mAh battery and it took just over four hours to charge. I'm waiting for my other B600BE to run down before I swap them over but, as expected, it seems that the second and fourth terminals on the pack are not required for charging. Assuming, as with most batteries, one is for a thermistor, what is the other for?

P.S. When I put the battery back into the phone it was only 87% charged even though my ‘intelligent’ charger thought it was full charged.


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## Felim_Doyle (Oct 1, 2013)

Here's a quirky battery, the BML-3 for the Nokia 3210. It's a 2.4V 1100mAh NiMH unit with a third ‘springy’ terminal on the side. In use, this third terminal makes contact with the chassis of the phone and so does not appear to have anything to do with a thermistor circuit. Does anyone know what it is for?


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## HiVoltage480 (Oct 8, 2013)

Felim....I am stumped as to what 3rd terminal of your nokia is for, but here's a bit more insight on terminals 3 and 4 of cell phone batts. Oh, firstly, you seem to have answered your own question as to what terminals are needed to charge batteries externally. Its just the positive and negative terminals that are needed as you stated, and any 4.2 volt, 500(or lower) mA trickle down charger will suffice. As to terms 3 and 4, which are sometimes labeled T and D, T is connected to an internal temperature sensitive component ( thermistor) . This is to prevent overheating of the battery. D or Do is a newly introduced contact. It is a data line which allows smartphone and battery to exchange information about current, voltage, temperature, residual battery capacity etc.... It has been introduced to improve % remaining battery capacity readings.


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## Felim_Doyle (Oct 14, 2013)

Ta-da!

Now it all makes sense (apart from the quirky BML-3).

Thanks, HiVoltage480.


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## Александр (Dec 18, 2014)

Felim_Doyle said:


> Well the B600BE is a 2600mAh battery and it took just over four hours to charge. I'm waiting for my other B600BE to run down before I swap them over but, as expected, it seems that the second and fourth terminals on the pack are not required for charging. Assuming, as with most batteries, one is for a thermistor, what is the other for?
> 
> P.S. When I put the battery back into the phone it was only 87% charged even though my ‘intelligent’ charger thought it was full charged.



Which charger did you use? I am currently buying chargers to compare for best battery charging, so I wish to avoid buying the charger you're referring to. Thanks.


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