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I'm trying to replace my tablet li po batteries and am trying to understand the connections. The following figure shows the 2 3.7v batteries connected in series. Most replacement batteries I've seen have just 2 wires coming out of them. I understand I connect them to the +ve and -ve contacts on the PCB. However, I'm wondering where do the black wires coming from the PCB connect on the battery and what is their purpose.

Also what is the whitish gluish like substance that covers the black wire connections on the PCB

The tablet is Fujitsu Stylistic M532 and the battery part number is FPCBP388

batteries with pcb

Below is the back side where the battery tabs connect to the PCB

backside

Closeup of where the black wires go into the battery. closeup

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Nas
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1 Answers1

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The black wires are connected to a thermistor on the end of each. The white goop is heatsink compound. They are used to monitor the temperature of the cells in order to provide a thermal mechanism for detecting full charge as well as part of a safety mechanism to prevent the cells from igniting.

Ignacio Vazquez-Abrams
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  • Thank you. Just to make sure I understand, I need to buy replacement batteries that have a thermistor contact as well? And after I connect (solder) the black wire to the thermistor contact on the battery, I need to coat it with the heatsink compound. – Nas Feb 17 '15 at 18:23
  • Also, if I don't find a battery with 3 wires, can I just connect the two wires to +ve and -ve and just leave the black wire unconnected. Will that still work? – Nas Feb 17 '15 at 18:43
  • I'm having trouble finding a tablet battery with 3 wires. On the other hand I can probably find cell phone batteries that have 3 or 4 contacts. Can I substitute the cell phone batteries for the tablet batteries – Nas Feb 17 '15 at 21:24
  • There aren't 3 wires to the cell. There are two wires to the cell, and 2 wires to the thermistor. You don't need replacement batteries, you need replacement cells. – Ignacio Vazquez-Abrams Feb 18 '15 at 01:53
  • I''m a bit confused. How is the thermistor attached to the cell. From what I read online, the thermistor is for monitoring the temperature of the cell. So it must somehow be "connected" to the cell. Could you maybe point me to where I can find more info – Nas Feb 18 '15 at 14:48
  • The heatsink compound thermally bonds the thermistor to the cell. – Ignacio Vazquez-Abrams Feb 18 '15 at 15:33