Why do MOBILE BATTERIES have THREE terminals? A simple Explanation. 

This video was exactly what I needed, I have an old phone with a dead battery and no charger, 6 minutes just saved hours of googling. Thank you!

The third pins explanation is nice, thanks. In regards to pin 4, at least on many Samsung phones, that's for nfc as the nfc coil is in the battery on those

Lithium Ion batteries not only catch fire/explode when they overheat. This can also happen at impact, short circuit and having the lithium metal react with water. It all potentially makes it go ablaze.

Battery protection is very important. A friend of mine bought a shady battery like this for his phone several years ago. The thing swelled the first time he tried to charge it. The battery was provided to me for the purpose of investigating what went wrong. Turns out the only "protection" there was a 0 ohm link where the double mosfet was supposed to be, and a no name npn transistor in place of the DW01 chip. Guess they used a PN junction of the transistor in place of a thermistor. Having said that, this third pin on cellphone batteries actually predates lithium ions. I've seen it on stuff used in the late 90's and early 2000's. I recall taking apart a Siemens C35 NiMh battery that looked almost identical to a Li-Ion battery. Inside however where 3 square NiMh cells in series, and the middle pin was nothing but a thermistor connecting to the negative pin. That was the whole electronics inside, and the thermistor played an important role in the charge of the battery, as that's how the charger was detecting that the battery is charged. When these batteries recharge to 100%, passing more current through them heats them up. That's what the charger detects, and stops the charge.

Yeah, I'm running my "Lenovo A2010" phone from an external 4.5V power supply since a month now and the phone itself is nicely stable. 🙂 Yes, a 10KΩ resistor between negative and middle pin is required, but also... ● two parallel capacitors between positive and negative to simulate battery capacity ● one series diode on the positive connector to limit current and preventing the phone from trying to charging the non-existent battery ● connecting the USB to a charger is also required, because the non-existent battery can reach below 1% over time because of software reasons So, actually, you can try this at home. 🙂

On some Canon camera batteries the fourth contact is to prevent third party batteries. The camera might still work but it may have limited functionality like not telling the remaining charge or it might just warn of the non-original battery. Some of those have been cracked though

i had always wondered why cellphone , digital camera , digital radios etc. have more than two terminals . he speaks clearly , not too fast and has the camera close to everything and it is focused good and he explains everything well

Thermistors were present before lithium batteries were used. If you check the battery packs on power tools, even the old ones with NiMH or NiCad always had at least an extra connection. You can also find batteries with even more connections for smart charging using a BMS (Battery Management System). The BMS can be in the charger or the battery (depends on the design).

What? I thought it was obvious: the extra connection pads are there to keep the magic smoke inside! Jokes aside, it never occured to me there was a thermistor involved. Thank you for demistifying this concept, also there are great comments in the comment section which go into other details, overall very informative experience

That's pretty interesting, although most Samsung batteries (not for newer phones, that's a separate component) have the NFC coil integrated into it, that is the case with the Samsung Galaxy s5 for example, that's probably why it has 4 pads instead of 3 pads.

Thank you for this great illuminating video, all i can say is that i'm all 'Charged up' after watching this presentation 🙂

excellent explanation which confirms what I always thought SHOULD happen, excepting cheap knock-off batteries of course. Thanks for sharing and great research, thank you.

I try to learn something new every day and here it is 8am and I've just done so already. Great content.

Dedicated camera batteries also have that protection feature with extra pins. Even shown at 4:30 in the video, but not quite pointed out in the dialog explaining this.

Ну да, очевидно это оказался термодатчик… Просто и логично! Спасибо!

Well Done, Ron!! Awesome delivery and production. You have most likely, saved lives. 😍😍

Sometimes the OEM batteries aren't that much safer! The photo you show of the protection board is a standard protection board that you'll see atop MOST batteries, its a DW01 chip and another bigger chip which is a MOSFET(switch). Their job is to disconnect the battery if its short circuited, discharged below 2.5V or charged above 4.2V. With these in place, batteries are much much safer - and 18650's often have them built in, but some, particularly lithium polymer rectangular batteries don't and these must only be used where there is another battery management system in place. None of this matters if the battery sustains mechanical damage which can then fail with spectacular results.

You helped me figure out how to hardwire a restaurant headset to a power source instead of needing to use a battery. I can already hook it up to a speaker. This way people on the line can hear the orders easily even though we only have 3 batteries. Thanks man

This is probably the most helpful video on batteries I have seen to date. May the algorithm spread the word.

Awesome video, can't believe your channel has such little attention, the quality is better than channels 40x the size!

Thermistors were already present on ancient Siemens' and Nokia's battery packs when they still consist of AAA or similar-sized NiMH elements.

What a relief. I've been asking myself this question for for years. Thank you very much for the explanation!!

Oh my.. this random video suggested by youtube will save me n my family from future mishaps. May nature bless you, sir 🙏

As a student studying electronics and working on circuitry, this is all 100% true

Outstanding!! I'd always assumed it was for data transfer! That's a handy thing to know. I was just wondering how I could get a thermistor without ordering one. Kudos!!!

Only one sentence for this clip,brilliant and clear explanation .

sir, today you teached a complete stranger a couple of things about batteries. Thank you.

2:01 What you said is indeed true for iPhone batteries over the past 5 years or so. iPhone batteries have some software mechanisms to prevent people from normally using a 3rd party battery. If you use a 3rd party battery for your iPhone, you will get a bunch of warnings and removed functionality of the battery. Apple is forcing consumers to only use official battery in their iPhones, which a serious issue for right to repair. You can’t even copy the information of the old battery and paste it onto the new one. The iPhone will still recognise the new battery as a 3rd party one. You need to buy a core battery, remove the battery management system (BMS) from the original battery, solder the BMS to the new core battery. All without frying anything. This is the only way to properly use a 3rd party battery on an iPhone. This shouldn’t be the case in this day and age. While the 3rd terminal is not use for forcing consumers to use original batteries, Apple does that by other means. There are quality 3rd party batteries in this world, we shouldn’t say no to all 3rd party batteries. But I do understand that there are unsafe batteries from China.

Fantastic Ron!. I'm sure others have explained those extra terminals. But your presentation is top notch. It would be interesting to see if you could figure out the extra terminals of laptop batteries. I scavenged many and in so many instances that tiny board caused the battery to be rejected as a faulty one. But when I measured the voltage of individual cells sometimes all of them were fully charged at above 4V. beside the temperature of the battery which is reported to the laptop, I suspect that at least one terminal provides the signature of the cell because my laptop recognizes the cell manufacturer and its part number. Moreover because of the laptop internal charger, it would make sense that many pins would be assigned to function as BMS. However the laptop does not really need to know the SOC of each individual cell... or does it? Just like the power supply sends a good signal to the PC, perhaps the laptop tests the SOC of each cells when it's first turned on, to make sure the battery is not faulty. The total voltage of the pack could still be good while the voltage of individual not meeting safety spec? The laptop could easily analyse if that's true, but i doubt that's the case as a hardware approach from the internal BMS can easily handle this task. Are you up to doing one of those laptop pack demystifying? Thanks

It seems counterintuitive that if the battery temperature goes up, the resistance gets lower. I learned something new. Thank you.

Ron. Thank you! I am not technical but you were able show and explain so that I understand completely. I'm never buying a cheap battery again!

Excellent video ! This is exactly why I had to use the protection board off my S4 battery to create a huge DIY battery pack 👍😆

With some phones that third pin can also be used to boot into service mode. And if someone wants to run phone using a external power supply, add some tantalum capacitors close to power pins. It will help with high power draws when cellular modem starts transmitting.

I have often wondered 'Why do mobile batteries have 3 terminals'? RU-vid served up this vid out of nowhere. Ty RU-vid, Ty Ron. I can now safely test many questionable batts and you have instantly allowed me to power a dozen old cell phones that I can use for cams, remote speakers, etc. Wow. Yep. Awesome vid Ron. Ty.

This just have solved the mystery about that pin incredibly well. Thanks a lot

Thanks for this high quality video. Also, good explainations on the parts that might be logical for people with a technical background but are not for beginners like me :)

Дякую за інформацію, все коротко і зрозуміло.

If I get to boot up my phone thanks to this, it would be great ! God bless this simple explanation and fix.

I don't know why this showed up in my feed, but I'm glad it did. That was some great info.

a video in an era where most phones have fixed-in batteries 😂

Thanks for the video! I always assumed the middle connector was for charging the battery.

This is occurs for semiconductor. If you heat a diode it will more conductive and if you cool it will loss conductivity. I had an experience of operating phones without middle pin. In my childhood, i was use my sister's ignored phone with torchlight's battery which had only two pins. So i think that is not a currect explanation. I expect that you will share content with more resources and knowledge. Good luck.........😊

The third terminal can sometimes be a serial bus using Dallas 1 wire protocol to a gas gauge IC. This allows reading current, voltage, temperature, battery serial number, max capacity, charge level and many other things. Sepura TETRA radios have batteries where the third terminal does this.

Fake/counterfeit batteries are indeed dangerous, but sometimes even genuine batteries can catch fire or explode if they were not built correctly: the Samsung Note 7 is a perfect example of this😮

wow, an explanation so simple even i can understand it. well done!

“Most people are positive”. Nicely done!

Дуже влучне пояснення теми, буду його рекомендувати;)

The protection mechanism must be implemented by the mobile phone and the battery to ensure safety

All depends on the third party battery manufacturer. Some might be better than the OEM.

This is really an intuitive video and clearly explained, thank you, I was wondering why there is a third pin since I was 7 years old, now im 18, finally learnt it after 11 years, thank you

very informative! had this small question for years. Now I will try if my new battery has at least a thermal resistor before using it. thank you!

I am amazed that you have only posted a handful of videos! Keep it up!

Ah yes, I remember having phones with replaceable batteries...

பாராட்டுக்கள்! Congratulations! Very Excellentastic Video! Thanks Mr.Ron Mattino!

Thank you for solving my childhood mystery

I worked at RadioShack back in the day. A customer lost his battery and we didn't have any. I was able to boot up his phone using 3 AA batteries but it didn't need a resistor. Strange but cool! Great video

thank you sir for sharing your knowledge. your youtube channel is a real treasure.

I subscribed.. Seriously this is just a simple video but very informative..thanks dude..

The middle connection communicates with the phone, whether the user is on blacklist, or not. Games can increase the battery power using this connection, by starting the game, and leave at the intro screen as the batt drains to zero. Turns on power management. Using gps map, localizes the battery, and uploads data, that the user is allowed to use the gps. Legal windows is recognized as Google Play store, before pairing with Bluetooth. Bt pairing and some file transfer keeping 5 m , enables bluetooth localization. After this, you have to start Google map for each battery, to localize the phone. Now, you can use the map and radio. Handy trick for outdated phones.

u can see on the PCB P- T P+ ez this is the reason why marking on PCB is very important

This is why OEMs need to make parts available

Was expecting maybe a 3.3v output on the 3rd connector, but of course it's a temp sensor! Really nice idea to put the teperature sensor inside the battery. Learnt something new about something I've never thought about, nice. 🍻 Thanks for this video.

Thanks mate! The couple of times i thought about what the pins were used for i just brushed it off and forgot about it but this video has been very informative. I liked it a lot!

The third pin goes to the thermal resistor which stops the battery from charging if it gets too hot. They used to put a "T" on the battery to indicate this, but most people don't really care as long as the battery charges and works.

Thanks man, subbed. I wish you grow big and share more wisdom.

That was really informative ❤

I think that when there are 3 inputs on a battery, the middle is for the ground cable (protective cable) but it is not used everywhere

Never a 3rd party battery... The worst you can do is to use fear to manipulate people. Nicely done.

Muito bem, irmão. Eu já sabia disso pois estudo eletrônica, mas muitos são ignorantes no assunto. Continue, e saudações do Brasil.

I actually have a nokia phone with a knock off battery that doesn't have short circuit protection. I bought it very cheap on second hand shopping site. I bought it to use it on school because my school doesn't accept smartphones with cameras and i use it every day. I didn't have any problem with it yet but i don't think the battery in it is safe i think i will replace it with a good one soon because i'm a little bit scared that it might explode if something goes wrong..

I did like this! I've always been curious about those extra pads, but didn't know whom to ask.

I always assumed it was some sensor or data but never bothered to figure it out. Thanks for the interesting video

Cell protection? Ok ! Thanks for your help Mr. Mattino. :) 🇧🇷

I use these batteries on a certain side project, I added a overcurrent protection, but now I will add a temperature protection too

I've noticed this on other batteries too, thank you for addressing all of them. :)

Gladly, not all electronic gadgets rely on a sensor reading, and it may be seen as "optional". I have a trusty old Gopro Hero 4 Black. I like to take this camery on long bicycle trips and have it running all the time, as some kind of a dashcam, mounted to the frame. However, original batteries last only around 4 hours - they also have 3 contacts. So my rides last for many hours. For whatever reason (I suspect firmware issues), the camera can be charged via USB, but when I start the recording, it stops taking power from USB and drains the battery. Tried it with many powerbanks, it just doesn't work. So I went the DIY route. I dismantled a dead 3rd party battery, took out the actual power cell and kept the body of the battery. I modified it, so that + and - wire were attached to the 2 of 3 contacts and also modified the camera frame, so that I can put that battery dummy into the camera and have those cables come out. Those cables connect to a battery holder, which contains 4 18650 cells. A Gopro battery offers something around 1,000mAh, those 4 lithium cells offer something around 10,000mAh. They are all connected in parallel, so all 4 together stay at the required 3.7V and the camera now runs up to 8 hours with those. Without the camera having any resistence feedback. But yes, you need to be careful. The battery holder remains in a way, that all 4 cells can be taken out to be charged individually, since charging all 4 together via the Gopro's charging current takes forever. And you need to watch out for polarity. A few times, I actually put in a battery the wrong way, instant smoke let me know about the short circuit and I quickly removed it again. But already within those 1 to 2 seconds, the batteries warmed up. Gladly, getting only warm caused no issues. But if I let them in there for something like 10 or 20 seconds, they may blow up. And for those who may have question marks over their head: Short circuiting is, when connect batteries in an actual circuit - attaching + poles to - poles and vice versa. Energy can flow without something in between, that actually uses it. But like in my contraption, all the +poles gets connected together and the -poles as well, energy can flow too - but only evening out. If one battery is 3.8V and the other one is 3.6V, they will even out to both be 3.7V. Basically you could say, one battery is charging the other one slightely - because that is how batteries get charged. A higher power value is connected to the battery, than the power level of the battery itself, connecting + to + and - to -. However, you should not combine full and empty battery, because that isn't too healthy for the batteries and just wastes energy.

This type of explanation and only this much views,subs? RU-vid content is often underrated or undiscovered like the oceans.

I'm stoked i finally know how to rum a phone without battery. thank you

Magnificent. God Bless you and the all the developers of RU-vid.

This is a great video. Thanks for making it. I've bookmarked it to watch again. I think I'll be avoiding dodgy third party battery manufacturers. Being able to power a phone from a difference source could be very handy if the battery stops working and I have to get data from my phone.

Thanks. Finally mystery solved 🎉

I thought all these days those were the power in terminal..like DC power input and output 🤯 thank you 🤙🏾

Dell used to do something like this, though. Their power supply for some of their laptops had a third wire running inside the middle connector. It was to send a signal to a part on the motherboard to let it know the Dell power supply was being used. If you got a power supply that had a matching voltage but no third wire, it wouldn't work. So sometimes when you ordered the right power supply, it still wouldn't work because the part on the motherboard was bad. It's called proprietary parts. Dell and others quit doing this practice to drum up after market sales because they found, as in this case, they were shooting themselves in their own foot. It was too expensive to replace the bad motherboards. Hahahah I love it!

Who remembers when the Boeing 787 Dreamliner first went into service with the first lithium ion main battery, which promptly caught on fire? The only thing that averted tragedy was the fact that the airplane was on the ground when the smoke began to leave the battery. Even airport fire fighters were unable to put the fire out until damage had been done to the airplane. The airplane type was grounded until Boeing figured out that they could not make the batteries safe. If you are a passenger on a 787, know that the battery is still the untrustworthy Li-ion type, but it is now encased in a vented metal box which is so heavy that it pretty much negates the advantage of using Li-ion in the first place.

Thanks a lot. All mobile phone users must watch this video. Very useful and informative. Thank you once again for sharing this info. God bless you.

Mobile batteries typically have two terminals: a positive (+) and a negative (-) terminal. These terminals are used to connect the battery to the electronic device's circuitry and provide electrical power to it. It is possible that you may have seen a third terminal on some mobile batteries, which is typically smaller in size than the positive and negative terminals. This third terminal is usually a thermistor, which is a type of temperature sensor. The thermistor is used to monitor the temperature of the battery, which is an important factor in the battery's performance and longevity. The thermistor helps to protect the battery from overheating by regulating the charging and discharging processes. If the battery temperature exceeds a certain level, the thermistor will send a signal to the device's charging circuit to slow down or stop the charging process, which helps to prevent damage to the battery and the device. In summary, mobile batteries typically have two terminals for power delivery (positive and negative) and a third terminal for temperature monitoring (thermistor).

Thank you for explaining, always wondered why they have another pin on the battery

For my 10 year old phone I purchase li-poly cell and reuse old bms from original battery :)

I was able to start couple of phones with only plus and minus terminal, but some phone wasnt charging, of course after connecting the middle it took charge, i wasnt thinking about tempareture stuff tho, Thanks for the video.

Every school needs him!

When my previous iPhone 5 battery puffed up, I went ahead and bought a third-party battery and for some reason, with that battery, I was only able to use it for a month before it stopped working. Luckily, I had my iPhone 8 before that situation. Until the beginning of 2021, I fixed my old phone and realized there was a problem with the battery, not the phone itself

Actually I short the middle pin to ground to turn my old Nokia On 🤣 thanks for the explanation Great vid!

When my old blackberry 7290 battery failed i ended up shoving a lipo and two resistors in it to keep it going. had four pins, one pin was for telling the phone what type and capacity it was and the other was for battery temps ( wont charge with out a connection ) worked well for many years after

The B.M.S. (battery management system circuit) is an important safety component of any lithium battery pack, it provides protection against overheating, reversed polarity, overloads, over charge and over discharge, if a lithium battery is discharged under certain threshold will not be charged (commonly under 2.5 volts) because for safety reasons any smart charger detect s it as faulty.

Running the work phone off a 18650 or two seems like a good idea. Delivery time , reliability and price of phone batteries compared to buying a tool battery from Aldi.

Yes old way is that NTC. Nowadays, especially in power tools, it is common for the battery and the device to talk to each other. In this case, the battery has its own microcontroller. In a few cases, I made a program for arduino that mimics the original battery.

Thanks baldy guy you earned my respect. Love from India

Even with all this technology (my phone has li-po battery), I never put my phone beside me on bed while it's charging. I just put it below the bed on floor. I did a stupid experiment in childhood which burst a li-ion battery. So I know how worst it could get. Never compromise on battery qualities

Amazing video! I never knew that batteries even had more than 2 connecters, until know, and I now I know why! Keep up the good work 👍

Now it makes 100% sense that the middle pin is oftentimes labeled "T."