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I have a series of three 3.7v 600mAh LiIon batteries powering a ca. 12v circuit. Currently, a DPDT switch rewires them into a parallel configuration when I charge them–each battery with its own charger module.

Incidentally I came to the idea that, if only the first battery charges, the other batteries will slowly charge as well (by the higher voltage of the first of the series). So it would be eventually possible to use the 12v circuit and charging the batteries (or at least not draining them) simultaneously.

Would this somehow work in practice?

enter image description here

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  • \$\begingroup\$ If you are careful to keep all batteries within their proper charge levels (neither over-charged nor over-discharged) the batteries do not care. Sounds complicated though. \$\endgroup\$ May 9, 2022 at 13:16

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This will not work as you wish. Instead, you will end up with the other batteries reverse charged and destroyed!

The charging current to battery one is being directed positive to positive and negative to negative. However, with the remaining batteries, these are connected positive to negative. The current flow is backwards (in terms of charging) on the remaining batteries which will continue to discharge until they reach zero volts. After that, as current continues to be forced through, they will try to acquire a reversed voltage which, depending on the battery chemistry, may have a catastrophic result but will certainly destroy any ability to be normally charged.

Conversely, if you connected one charged battery in parallel with several discharged batteries, the charged battery will try to charge the other batteries.

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  • \$\begingroup\$ Very interesting. I suppose the described behaviour responds to electrons flowing actually from - to +, contrary to (my) common belief. What would happened on the contrary, if only the last battery in the series would be charged? I mean the one closer to the Load (in the picture). Would the opposite happen (what I want)? \$\endgroup\$
    – Domingo
    May 9, 2022 at 14:39
  • \$\begingroup\$ Forget about my previous comment–it would short battery 1 and 3 the way I was imagining. I was just trying to find a way to charge and use a series simultaneously... Thank you for your contribution. \$\endgroup\$
    – Domingo
    May 9, 2022 at 14:53
  • \$\begingroup\$ no need to explain that a comment is erroneous ... just delete the comment \$\endgroup\$
    – jsotola
    May 10, 2022 at 1:07

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