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I have a 6-pack of 18650 Li-Ion cells connected in series, so it gives around 22v dc output.

To charge a single Li-Ion cell I need a 4.2v 1-1.5A charger, simple stuff. But to charge the whole 6-pack, do I still use 4.2V for all of them, do I use 25v, or do I charge all of them at 4.2v separately?

The cells are taken out from a single laptop battery, so they're identical.

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  • \$\begingroup\$ "The cells are taken out from a single laptop battery, so they're identical." No two cells are identical. That is why you should always try to charge them individually. Also charging cell, particularity Li-Ion cells, is not a matter of 'just' putting a voltage on them and push a current through them. \$\endgroup\$
    – Oldfart
    Commented Oct 5, 2019 at 9:10
  • \$\begingroup\$ Tell me more though, particularly: They aren't identical, so it's preferable to charge them separately. However it is possible to charge them all-at-once, right? If it's not a matter of "just" pushing current through them, then what it is? Obviously the overcharging safety measurements aside. \$\endgroup\$
    – almarc
    Commented Oct 5, 2019 at 9:13
  • \$\begingroup\$ Charging cells is a complex subject which can't be explained in a moment. You can learn a lot by putting "li ion charging" in the search bar. There are more then 1000 hits. My comment was mostly to warn you as there are serious (fire) risks if li-ion cells are mishandled. \$\endgroup\$
    – Oldfart
    Commented Oct 5, 2019 at 11:35
  • \$\begingroup\$ "The cells are taken out from a single laptop battery" - how old was the battery, and why was it dismantled? \$\endgroup\$
    – Bruce Abbott
    Commented Oct 13, 2019 at 2:41

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Since you have 6 Li-Ion batteries in series, you could charge them at 25.2V (Since the max charge for a Li-Ion is 4.2V * 6 = 25.2V). The current used the charge the cells depends on the battery itself. Batteries usually have a part number printed on them. So if you find the datasheet, then you can determine the maximum current you can charge the batteries at. It will usually say something like "max charging current is 0.5C" with "C" = the mAh rating of the battery.

However, when charging batteries in series, it is always recommended to use a balance charger. This is to ensure that all of the batteries are at the same voltage potential and no single cell becomes over charged.

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