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So I just found an old netbook which battery has 6x 18650-26F cells and thought of trying to make a powerbank out of them. This is the specs page: http://gamma.spb.ru/media/pdf/liion-lipolymer-lifepo4-akkumulyatory/ICR18650-26F.pdf

I just need some ICs and a bit of soldering to make them work but I still have some simple questions.

  • Which is the best configuration about parallel/series? So I can use a boost converter.
  • Should I need a battery management system for each pair?

Sorry for the basic questions, not much into electronics yet.

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    \$\begingroup\$ You may want to put off playing with grenades, I mean lithium batteries until you get a better understanding of it. They can explode. \$\endgroup\$
    – Passerby
    Commented Aug 28, 2018 at 14:50

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Your simplest solution would be all parallel. That way, there's no need for balancing, as there would be with a series string.

Equalise the voltages before connecting the cells in parallel, connect cells with resistors for a while to do this easily. This is very important, dangerous currents can flow if you connect unequal batteries directly.

Use a fuse per cell when connecting in parallel, to prevent a single battery fault becoming a disaster as the other 5 batteries gang up on it.

A boost converter up to 5v output would be needed from the 4.2 to 3(ish) (depending on your chosen endpoint) voltage range of the cells.

If you only want 5v at 1A, then a single 18650 plus boost converter will meet that requirement. Add more cells to last longer, or for higher current output.

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  • \$\begingroup\$ But will it still give me at least 5V at 1A? Ill be using the boost converter and some charge/protection circuit. \$\endgroup\$
    – Francisco Aguilera
    Commented Aug 28, 2018 at 15:03
  • \$\begingroup\$ I think it is dangerous advice to suggest connecting old lithium batteries in parallel, unless you emphasize very strongly that the cells must be equalized first and each cell should be fused. \$\endgroup\$
    – Elliot Alderson
    Commented Aug 28, 2018 at 15:27
  • \$\begingroup\$ No, if you tie them all in parallel, the nominal output voltage, per the data sheet, will be 3.7 volts. It will be the job of the boost converter to convert this to 5 volts. \$\endgroup\$
    – WhatRoughBeast
    Commented Aug 28, 2018 at 15:27

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