I made a power pack using 18650 batteries from an old laptop. All batteries tested individually are good. 4 batteries in 2S format. I used a cheap 2S 3Amp rated protection board I got on Ebay from China. I correctly connected all the terminals and properly soldered, B+/B- to the +/- of the final ends of battery and BM to the middle.

The voltage measured directly at the battery terminals (at B+/B-) is 8.4 volts but at P+/P- of the board it measures 7.5. Which means this board will not produce more than 7.5 volt usable voltage even when the batteries are fully charged to 8.4. Is that expected and normal? or is there a problem with the board.

Thanks for help.

  • 1
    \$\begingroup\$ What does the Datasheet for Protection Board say? \$\endgroup\$
    – Tyler
    Apr 16, 2019 at 22:47
  • \$\begingroup\$ What was the Vdc input? \$\endgroup\$ Apr 16, 2019 at 22:58
  • 1
    \$\begingroup\$ Failing the datasheet, look up all the parts, draw a schematic and predict what the drop should be. They may have cheaped out on the MOSFETs. \$\endgroup\$ Apr 16, 2019 at 23:08
  • \$\begingroup\$ This is a question for the datasheet or the seller. Voting to close as this site isn't the free help desk for cheap chinese sellers. \$\endgroup\$
    – JRE
    Apr 28, 2019 at 8:37

1 Answer 1


You bought a Chinese module from China on ebay. Enough said.


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