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I have this battery with it's own charge/discharge circuit. There are 5V out and 19V. The total capacity is 42000mAh @ 5V with 6 cells inside. (4.11V/4.12V each, fully charged). I don't know the capacity of each cell.

Green PCB showing three white battery packs with yellow tape and a USB stick device displaying 0.32A

Can I keep the PCB and replace all of theses cells for biggers, to increase the total capacity of the battery, knowing I need both (5V and 19V) output?

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  • \$\begingroup\$ That depends on factors like if the charging curcuit is depending on the batteries internal resistance. \$\endgroup\$ – PlasmaHH Apr 21 '15 at 12:14
  • \$\begingroup\$ Thanks, can I know it without the datasheet? (with tests for example), or if I get packs with the same resistance (sorry for my ignorance) \$\endgroup\$ – Guillaume Apr 21 '15 at 12:17
  • \$\begingroup\$ 4.11 is in range of standard voltages for a single charged Li-oin / Li-pol cell. \$\endgroup\$ – Dmitry Grigoryev Apr 21 '15 at 13:26
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If you increase the capacity of the cells, a well-designed charging circuit should handle them just fine, increasing the charge time as necessary. Decreasing the capacity would be more dangerous because the charge current would be too big for the new cells.

Whenever this particular circuit is well-designed or not is quite impossible to tell from the photo.

Some battery packs also estimate the amount of charge remaining in the cells. For such estimation current cell voltage is not enough, because individual cells have slightly different curves of voltage vs charge. To improve the estimate, your battery pack may use a hardcoded capacity value and/or estimate it during previous charge/discharge cycles.

Hopefully, this charge estimation doesn't affect the charge process, otherwise your cells may stop charging prematurely and you will never use their full capacity.

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  • \$\begingroup\$ Yes, it's a risk... Thanks for your answer, useful. If you say that's not impossible, I can go go ahead \$\endgroup\$ – Guillaume Apr 21 '15 at 13:01
  • \$\begingroup\$ Each pack (mesured by couple) is 4.11V, I modify my question \$\endgroup\$ – Guillaume Apr 21 '15 at 13:08
  • \$\begingroup\$ If the design includes software, even a "well designed" pack may not automatically adapt to larger cells without software changes (or link settings) for which there is probably no available documentation. \$\endgroup\$ – Brian Drummond Apr 21 '15 at 13:23
  • \$\begingroup\$ Good point. If the power bank uses a hardcoded nominal capacity to report the percentage of charge remaining, I would expect it to report inaccurate values. Do you think the hardcoded capacity value could affect the charge cycle as well? \$\endgroup\$ – Dmitry Grigoryev Apr 21 '15 at 13:30
  • \$\begingroup\$ I once owned a gadget which could fit batteries of different capacity. I remember it was suggested to leave the device without any battery for several minutes so that the controller would forget the estimated capacity of the old battery and reevaluate it during the next charge cycle. \$\endgroup\$ – Dmitry Grigoryev Apr 21 '15 at 13:34

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