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Mobile phone battery bus are usually 3 pin or 4 pin which are usually 2 wire buses (I2C) or a similar type of serial interface for a 1 wire bus. Does anyone know of a method for checking which bus type it is.

I don't believe a thermistor is solely used for Li batteries, that idea came from fast charging of other types of battery.

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    \$\begingroup\$ Hmm, all the 3/4 pin Lithium Polymer batteries for phones I have seen do use a temperature sensor (usually an NTC). There is no reason to use I2C or whatever as that would only increase the price. You make wild claims (I don't believe a thermistor is used for Li batteries) so I hope you're prepared to show some evidence. \$\endgroup\$
    – Bimpelrekkie
    Commented Nov 26, 2017 at 16:55
  • \$\begingroup\$ Which 3/4 pin batteries are you talking about ? Using a thermistor is pretty dangerous given there is no state of charge info from the battery. I did design charging software for Li cell batteries through I2C, so no wild claims on my part. Please show evidence of thermistor used. \$\endgroup\$
    – LateDev
    Commented Nov 26, 2017 at 17:16
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    \$\begingroup\$ heat can cause safety issues, and for safety and Samsung reasons .. no explanation is neccessary why safety and thermal sensors are needed. \$\endgroup\$
    – D.A.S.
    Commented Nov 26, 2017 at 18:25
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    \$\begingroup\$ If a battery uses some "smart" interface, usually it communicates with a sizable data acquisition/monitoring IC inside, which has the temperature sensor embedded and is a part of monitoring routine. \$\endgroup\$
    – Ale..chenski
    Commented Nov 26, 2017 at 21:07

2 Answers 2

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Mobile phone batteries don't use any "bus". The I2C-like bus is a feature of "smart battery", a different class of multi-cell batteries used in older laptops. These smart batteries need the communication bus because they contain "fuel gauges" and other control electronics inside the battery, so the laptop host can maintain and report the battery health status.

The mobile single-cell batteries can have 3 or 4 terminals. Older small cells (for cameras, other small gadgets, old Nokia phones, Motrorola flip phones) use 3-terminal batteries, with typical middle connection going to a thermistor.

The thermistor is an important part of Li-Ion chargers, to prevent cell overheating in cases of strong cell failure, which can lead to rapid "venting" with possible fire. For example, the entire line of BQxxxx battery chargers from Texas Instruments have a special input which should be connected to a thermistor network. Without having proper resistance (voltage level) on that pin the IC will signal fault condition and won't charge the cell. If someone wants to substitute the battery in some device with AC-DC adapter, this pin has to be emulated with proper resistor to ground (negative) terminal. The value of 10k is typical, but other values were used as well.

In Samsung (and other) phones the battery cell has 4 terminals. In some cases (original phones) these two extra terminals go to a printed near-field antenna that is glued to the body of battery. In replacement batteries this antenna may be omitted, sparkling outcry about "fake batteries".

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  • \$\begingroup\$ Interesting as ti.com/product/BQ27542-G1/datasheet used on the iphone. It has no external thermistor connection as that is internal. \$\endgroup\$
    – LateDev
    Commented Nov 27, 2017 at 23:40
  • \$\begingroup\$ @LateDev, recent batteries don't use naked terminals anymore, they use special hybrid power/signal connectors hanging on wires, and look more like as "smart batteries". The BQ27542 is "fuel gauge", with recommended attachment to external thermistor (buried within the battery), and the primary bus is "1-wire HDQ", according to its datasheet. So it is up to system designer how to partition the battery service on a product. \$\endgroup\$
    – Ale..chenski
    Commented Nov 28, 2017 at 6:16
  • \$\begingroup\$ its still a terminal regardless of it hanging on a wire and mobile phones still have sprung loaded contacts for connecting to the battery. As far as the BQ thanks I am aware of using an external device, I was just pointing out that there is no external battery connection needed for the thermistor as that is integral with the chip cct. The chip is either I2C or HDQ according to the spec. HDQ and I2C Interface Formats for Communication with Host System, Internal or External Temperature Sensor for Battery Temperature Reporting. Many thanks for the info \$\endgroup\$
    – LateDev
    Commented Nov 28, 2017 at 14:37
  • \$\begingroup\$ @LateDev, "... and mobile phones still have sprung loaded contacts for connecting to the battery". No, they don't. When last time did you open a modern phone? ifixit.com/Teardown/Samsung+Galaxy+S7+Teardown/56686 (unless you mean that every connector eventually uses some sort of springs). \$\endgroup\$
    – Ale..chenski
    Commented Nov 28, 2017 at 22:52
  • \$\begingroup\$ ChenToday actually and it has sprung loaded contacts for the removable battery. There is little point in pointing out a phone with a built in battery, and say look this is typical of all phones. Regardless of that the contacts are still +1 even with a fixed battery and it does represent a cost, when you are talking about thousands of phones. \$\endgroup\$
    – LateDev
    Commented Nov 29, 2017 at 14:59
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Notice that the specifications for the battery are on the label. e.g. Compliance: GB/T18287-2013, UL1642 and IEC61960-1

Note: China New GB/T 18287-2013 Standard of Lithium-ion Cells and Batteries for Mobile Phone and Smart Terminals

enter image description here

If you can find the relevant specs ( try really hard), it will tell you every parameter that the battery must meet.

Other info

https://www.mipi.org/sites/default/files/BIF_v1-1_Spec_Brief_20140807.pdf

This is a brief MIPI alliance spec used to define modern smart chargers.

The full spec is a paid document. There are many variables including temp sensors and data rate.

for more results...

This white paper may give some clues. http://introspect.ca/

For a decade, the mobile device industry has blossomed with approximately 1.5 billion mobile devices and at least 1.5 billion batteries per year using many different, non-standardized battery interfaces.

Now there is a standard. How it is used, where and which units, is a million dollar question.

The spec will amaze you, as it will be used everywhere power and peripherals talk to each other from chip to chip.

https://www.mipi.org/specifications

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  • \$\begingroup\$ I wouldn't be so sure about "will be used everywhere". The keyword, as usual, is "cost". Power Delivery is one good example, there is a standard, but most makers go with simple QC method. Another big example is OTG - VBUS pulsing, several methods of "session control protocol", other baloney. The end was a single ID pin, floating or grounded. That's it. Also, it does look like there is little business case to have batteries standardized. Batteries are expendable, so profit margins on them seems to be quite good for proprietary manufacturers. \$\endgroup\$
    – Ale..chenski
    Commented Nov 26, 2017 at 20:59
  • \$\begingroup\$ Based on ACPI which is universal to all PC's, MIPI DisCo will become universal to all Mobiles for any OS. \$\endgroup\$
    – D.A.S.
    Commented Nov 26, 2017 at 21:36
  • \$\begingroup\$ Maybe. But ACPI was introduced (pushed on industry) by a company that has/had 80%++ of PC market. There was no alternative to that. And the documentation is/was open, unlike the paywall of MIPI. I am still skeptical. \$\endgroup\$
    – Ale..chenski
    Commented Nov 26, 2017 at 22:52
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    \$\begingroup\$ The reason I asked was because, many years ago, I was on a design team for a major mobile phone company that did use I2C for communication with its early line of phone batteries. The cost offset was extremely small in production to any other method and 1 wire bus was muted at the time. Thanks Tony for the information which is of course a 1 wire bus. \$\endgroup\$
    – LateDev
    Commented Nov 27, 2017 at 0:24
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    \$\begingroup\$ @LateDev, about twenty years ago there was a company named Benchmarq. They were bought by Unitrode, and TI bought the Unitrode. Since then the TI maintains a battery-charging product portfolio. Early product lineup included many ICs with "1-wire HDQ interface". ti.com/sc/docs/msp/sine_on/batt_mgmt.pdf I don't recall, however, this interface in current offerings. \$\endgroup\$
    – Ale..chenski
    Commented Nov 27, 2017 at 1:19

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