How would I charge an 18650 battery with a built-in protection circuit?

This is for an infrared camera. I normally could charging the device via micro usb but port broke.

4 wires are soldered to the PCB. I assume 2 are used for charging the battery and 2 are for powering this device. All wires go to a 4 pin connector which plugs into the device. The only hobby chargers I saw with you 4 pin ports were for charging 3S cells. I think connector is a male JST.

Here are some closeup shots of the connector.

PJ-100-D is printed on the other side of the circular board.

Thank you

Here is a picture of the board with the soldered wires

  • \$\begingroup\$ That's a dual MOSFET, typically controlled by the DW01-P, per the schematic in this post: electronics.stackexchange.com/questions/203463/… . Operation of the DW01-P is well described if you google it. \$\endgroup\$ Commented Nov 21, 2020 at 19:49
  • \$\begingroup\$ Are the two red wires soldered to the same pad on the PCB? Likewise, are the two black wires soldered to the same pad on the PCB? \$\endgroup\$
    – user57037
    Commented Nov 21, 2020 at 21:58
  • \$\begingroup\$ Yes, both red and and black wires go to the same pad. \$\endgroup\$
    – wigoe1984
    Commented Nov 21, 2020 at 23:16
  • 1
    \$\begingroup\$ The cables are probably doubled to increase the maximum current. This could be used either when charging or for powering the device, but there is nothing special about the fact there are two. \$\endgroup\$
    – David
    Commented Nov 21, 2020 at 23:53
  • \$\begingroup\$ Makes sense, is there a way to charge this with a hobby charger? \$\endgroup\$
    – wigoe1984
    Commented Nov 22, 2020 at 0:07

1 Answer 1


You should be able to charge it using the two wires with any Lithium Ion or Lithium Polymer battery charger. The circuit board seems to just be a protection circuit. You just need a charger with some sort of output connector (rather than the type designed for cells to be inserted in the charger). The capacity of the cell is probably 2 to 3.5 Ah. Charging at 1A or less should be OK.

  • \$\begingroup\$ Do any of these connectors “fit” the above pictured MOSFET? I am having trouble finding an output connector compatible with this plug. Alternatively, can I simply cut and strip a positive and negative wire (while leaving the 2 attached to the plug) and use those for low current charging? I am nervous about doing this. Thank you very much for the input. I’ve been look at output connectors like this: amazon.com/Battery-Charger-Connector-Splitter-Alligator/dp/… \$\endgroup\$
    – wigoe1984
    Commented Nov 22, 2020 at 4:12
  • \$\begingroup\$ No I don't think any of them will fit the JST connector. That is a hilarious product though. I can't tell from the photo but I think that is a JST PH series plug. You could solder something to these headers: amazon.com/Micro-Connector-150mm-Cable-Female/dp/B01DUC1S7S/… \$\endgroup\$
    – user57037
    Commented Nov 22, 2020 at 4:32
  • \$\begingroup\$ Yes, what makes it frustrating is that the thermal camera will only accept the male JST connector pictured above (it's a female JST on the board). I would love if it were something else. I will continue to explore my options. Thank you very much for all of the help! \$\endgroup\$
    – wigoe1984
    Commented Nov 22, 2020 at 5:11
  • \$\begingroup\$ So the battery has the plug and the camera has the header. So that means that to charge the battery you need a header (what you are calling female). That link has both genders of connector anyway, though. So the trick would be joining wires from the charger to the header which is intended to be installed on a PCB. It is not clean but it can be done. Also, any 2mm header will probably work, as long as the pin diameter is not too large for the plug. The JST header is shrouded and enforces polarity. But you could conceivably just use a bare mm header (if you are careful). \$\endgroup\$
    – user57037
    Commented Nov 22, 2020 at 5:22
  • \$\begingroup\$ Yes, in normal operation the camera would charge the 18650 when connected to its USB charging port. The charge would pass through the JST and into the battery. Since the USB port broke, there was no way for it to charge from within the camera. That is why I was looking into external charging options. Both the male/female JST port are working. I realize that my original question may not have been clear. Thank you for the clarification and help. I understand a lot more now. \$\endgroup\$
    – wigoe1984
    Commented Nov 22, 2020 at 6:03

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