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I have 4 x 1Ah Lithium Ion battery packs. These I have two systems, one operates at 5V (usb) and the other requires 20v - 24v. I'm wondering can I power both the 5v system and the 20v system by using one USB port on the unit normally, and the other to wire the batteries in series? or am I misunderstanding the principal. Also, would this affect how I charges the batteries? or could I charge them normally using the micro USB.

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    \$\begingroup\$ Yes. Pick GND of one port as a 0V reference and chain VBUS to GND of another source (and again and again). VBUS of the first one will be at 5V, VBUS of the fourth at 20V with respect to the 0V reference. Of course the first one will be drained faster. For recharging, it is necessary to disconnect everything and charge each one individually. (Actually if the whole system is not earth referenced, it is possible to charge on the run, one battery at a time) \$\endgroup\$ – venny Sep 20 '14 at 22:20
  • \$\begingroup\$ @venny - That seems like a complete answer. \$\endgroup\$ – gbulmer Sep 20 '14 at 23:37
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You can, but there are a couple concerns.

You will definitely want to disconnect them from each other before charging - otherwise they may all end up connected to the same ground point and causing a short.

The picture looks like the cases may be metal. If so you need to check if ground inside is connected to the case. If it is, you need to make sure the cases don't touch each other,because you are hooking positive of one to ground of another, the cases touch would make a short.

If the 5v circuitry draws any significant amount of power, its battery will drain much faster than the others, so it may die long before the other packs are empty. Those packs may even cut off entirely when their internal battery gets too low, so one pack getting too drained will shut everything off.

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