Why 4 contacts on cell phone batteries ?

[TooManyGizmos]

:thinking:
It dawned on me that all cell phone batteries I've seen have 4 contacts rather than two.


Can anyone tell me why that is ?

Thanks

 

[EngrPaul]

Redundancy.

 

[mdocod]

mine has 3 go figure...

IIRC, on some phones, the "vibrator" is in the battery, so it needs some extra contacts to control that.

 

[Patriot]

Mine LG is also 4 contacts....no vibrator battery on mine. Redundancy makes sense to me I guess.

 

[Norm]

Perhaps balancing taps?

 

[ICUDoc]

Perhaps it has three cells,so two contacts for + and - (from the outside two cells), and two for reading the charge state of the cell "in between" the outside two. This gives a safer way of charging LiPo cells, as Norm says. I wonder if it is possible that they use some of the cells to provide a lower voltage tap? Why not measure the voltages with a multimeter?

 

[linterno]

Those are smart batteries and those two or one additional leads are for reading battery state (temperature, voltage, capacity, current charge state and some other information).

The hardware protocol used by the phone to get information from the battery is SMBus.

 

[EngrPaul]

I took apart an expired PDA cell once, and found that all four connections lead to two wires. It could be different by model.

 

[shadowjk]

Some just have a temperature sensor on the third lead.

 

[EngrPaul]

I found a cell that has three. They are marked as follows:

(+) (T) (-)

 

[UnknownVT]

I found a cell that has three. They are marked as follows:
(+) (T) (-)

Slightly OT - Canon camera proprietary Li-Ion batteries also have 3 contacts marked the same way -

The NB1LH was used in the earlier tiny Canon Digital ELPHs
The NB2LH was used in the Canon PowerShot G9, G7, S70 and S80 - and the Digital Rebel XT & XTi dSLRs, as well as several Canon camcorders.

 

[VidPro]

one of them is (sometimes) used as a DATA from the battery, for info, similar to infolithium used by sony. with series cells (like camcorders) it could be a centerTap, but it usually is not.
depending on the sofistication of the curcuit (which also has the protection) they can determine the actual miliamps of use, and provide the user with a (supposedly) better view of how far the battery is discharged. AKA 1/2 of it left. just like laptops and cameras , they dont nessiarily get implamented, arent nessisarly on cheap replacements, and only work as well as the battery itself, and its known calibration.

some of the batts have thermal probes, connected to the same curcuit, or sitting ON the curcuit in the smaller ones.

an example, some of these curcuits have a known capacity ingrained IN the curcuit, say 1200ma , and when it sees 600ma leave, it figures there is 50% there still, mabey there is mabey there aint but at least they try. when you change the Cell, and use the SAME curcuit, it still works, but it still thinks its the 1200ma battery that was originally there, or say it will only go to 2000ma. stuff like that.
it Can be knowing more about the battery, and send that info to the "computer".

once you go with a Knock-Off , a lot of that stuff can be wrong or not even in existance :-(

 

[jzmtl]

My motorola battery has 4 contacts, only two outer ones will produce a voltage reading if I recall.