I have a collection of 4 LC18650 batteries. I need to draw at least 12V with a current of at least 1 amp, hence the use of lithium batteries. I know I could use lead acid but environmental impact, energy density, and compactness of the system are high priority concerns. My best option is to use 3-4 lithium batteries connected in series.4 LC 18650 batteries in series

I also have a battery holder that connects the batteries in series to output the combined voltage. At full charge, the bank should output ~16.8v, and ~12.0v at low charge.18650 4x1 holder

My understanding is that doing this wouldn't be a problem, however recharging the batteries without removing them would be. I personally find the idea of removing the batteries in order to charge them distasteful and unprofessional, but keeping them from exploding is much more important. To that end, I've acquired a BMS from my local electronic component store, which unfortunately did not supply a datasheet. BMS FrontBMS Back

As I understand it, I connect the 0v pin to the negative terminal of the first battery. I then connect the 4.2v pin to the positive terminal of that battery and the negative terminal of the second battery. I repeat this for all remaining batteries. Next, I connect the 0V pin to the ground supply of my device and the 16.8v pin to the V_BATT connection. I can then charge all the batteries from said device exactly as I would a single battery. Is my assessment accurate? How exactly does my BMS work? If I'm wrong, how would I design such a system?

  • \$\begingroup\$ what series is the BMS? i.e. 1S 2S 3S 4S... \$\endgroup\$
    – user256116
    Dec 10, 2020 at 23:39
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    \$\begingroup\$ Well, I find the idea of an electronics store selling you something but unable to give you instructions or a datasheet distasteful and unprofessional. \$\endgroup\$
    – Finbarr
    Dec 11, 2020 at 0:51
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    \$\begingroup\$ That's not a BMS it's just a balancer. The cells have tabs which are supposed to be soldered together (and to the balancer). Soldering (if done properly) makes much better connections than a holder. \$\endgroup\$ Dec 11, 2020 at 8:46

1 Answer 1


Almost certainly [tm]:

The 4S battery string has 0V at most negative and +16.8v at most positive end.

Total of 5 connection points - ground/negative and top of 1st 2nd 3rd 4th cell.
Connect most negative to 0V,
1st top to 4.2V,
2nd to 8.4V etc.
There is a very very very high chance of this being correct.

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