# identify terminals of a 4 terminal battery?

i have an old mobile phone with a 4 terminal battery
the end terminals are labelled "-" and "+" but the middle ones are labelled as "CF" alongside negative terminal and "VF" labelled alongside positive terminal.
what do these two terms mean and why are they there?

battery is 350mAh 3.7V battery.
i dont have a multimeter but i checked the resistances between terminals (using an LED) as

terminals                      LED brightness                                             Remarks
+ & -                          (more than normal brightness )                  no resistance
+ & VF                       ( normal brightness)                                     some resistance
+ &CF                        (less bright )                                                   more resistance

in the image from top to bottom alongside golden color terminals labelling is as

-            (in picture as P-)
CF

VF
+          (in picture as P+)

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3 years ago

During Stage 1 (constant current charge), the charging current is kept at a constant value (I const) until the battery voltage reaches the final cell voltage (VF). Note that the battery could suffer significant damage if this final voltage is exceeded. Then, in Stage 2 (constant voltage charge), the voltage is kept constant within this limit by slowly decreasing the current.
Charging is stopped when the current drops below the manufacturer fixed threshold value (I SAT). This current indicates that the battery is saturated.

MYawar (author)  petercd3 years ago

Also i asked this question cause i am modifying my 4 pin phone to work with 3 terminal battery, the battery charges well and gives good standby time as well upto a week but the problem is that it doesn't give a low battery signal or alarm but abruptly shuts down, I am using (nokia BL-4C 860mAh and 3.7V 3-pin battery) the pins on it are labell3d as ( +,o,- ) i dont know what "o" means ,

is there any way solve this low batteryalarm problem?

thanks for help_

3 years ago

That pdf was a long read and I wasnt really that into it, but I seem to recall something about Charge Final, when its reached the level.

solve this low batteryalarm problem?

other than using the correct batt for the phone... nope, that would need a new circuit design.

modifying my 4 pin phone to work with 3 terminal battery

li-ion batts dont take kindly to messing with their charge rates, which as an industry standard was integrated into the device and not the battery.

meaning dont take one batt and put it into another device with an entirely different application/ charge rate.

MYawar (author)  petercd3 years ago

Thanks that solves my problems, and i will be restoring the phone back to its original condition ASAP

mpilchfamily3 years ago

The additional pins are for the charge controller to monitor the battery.