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I'm looking a this to write my own charging algorithm (really not looking to re-invent the wheel here) and have been referencing this article: http://powerelectronics.com/site-files/powerelectronics.com/files/archive/powerelectronics.com/mag/504PET23.pdf

It'd be easier in this situation if I just jump straight to stage 2, constant-current charging at 0.2/h*C to 0.7/h*C which makes me wonder just how important that first stage is and what its purpose is in terms of the battery chemistry.

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When Li-Ion batteries become the discharged the ESR rises significantly. Therefore when charging with a high constant current the battery does not charge efficiently with a high constant current and risks over-heating from the high ESR. Therefore you must use a lower CV rate until the battery ESR drops at a certain charge level or voltage level then CC mode can resume. Excess heat can cause excess forces inside from outgassing but also internal excess temp causes premature aging.

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    \$\begingroup\$ I'd like to second this. Pissing off LiPo cells causes fires. Follow all the specs! Also, I've found LiPo cells to not really be recoverable when they're depleted too much -- a cut-off at 3.2V is reasonable, and trying to charge when cell voltage is much below 2.9V or so gets diminishing returns. \$\endgroup\$ – Jon Watte May 1 '14 at 0:21

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