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Cell Phone Battery Project?

I am planning to use a bunch of 3.7V Li-ion Cell Phone batteries for a project I am doing. I am somewhat baffled at why it has four electrical contacts...I would charge them and figure out the poles, but the cell phones that held the batteries are long gone and I don't want to have to solder more than once. Thanks for reading.

3 Answers

  • Numbat
    Lv 6
    1 decade ago
    Favorite Answer

    Li-ion batteries are somewhat different to other cells. It is possible to cause them to ignite by charging them incorrectly. Even without charging, there have been cases of batteries igniting without the owner doing anything. There was a recent recall by a well known manufacturer recently for this reason.

    The extra contacts are for safety circuitry and monitoring.

    Inside a Li-Ion pack there is always a safety circuit that consists of four main sections:

    1. The controller IC that monitors each cell (or parallel cells) voltage and prevents the cells to overcharge or overdischarge controlling accordingly the cutoff switches. Also the voltage across the switches is monitors in order to prevent over current.

    2. The control switches that usually comprises FET structures that cutoff the charge or discharge depending on the control signals of the controller IC.

    3. The temperature fuse that cutoff the current if the control switches experience abnormal heating. This fuse is not recoverable.

    4. The thermistor (usually PTC) that measure the battery temperature inside the pack. It's terminals are connected to the charger so it can sense the temperature of the pack and control the charge current until the battery it's full charged.

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  • Anonymous
    1 decade ago

    If there is no voltage at all on any combination of contacts, your battery is dead. You need to find a newer one that still has some life left.

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  • Anonymous
    1 decade ago

    there couple things you can do get a multimeter anf find the + an - or get a LED and check them

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