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Rapid charging of “energy cell” (e.g. lithium-cobalt) type Li-Ion batteries, say at 2C, 3C or higher, is well known to reduce battery lifespan.

On the other extreme, does charging at very low rates, say C/10 or C/20, have any effect on their lifespan?

For instance, I charge my portable devices such as phones and tablets using a 2.5 W charger. My thinking is that any extra time spent charging is time not spent discharging, which would contribute to extra cycles on the battery, as well as slightly reducing temperatures, since high temperatures are also known to be detrimental to battery lifespan. I also use limited-wattage-output power banks to (very slowly) charge my laptop battery while away from a power outlet.

While the effect on these variables may be minor, it should be beneficial or at most irrelevant. What I’m looking for are any references to detrimental effects from slow charging.

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  • $\begingroup$ Why people keep thinking battery lifespan is a chemistry issue? $\endgroup$
    – Mithoron
    Oct 20, 2022 at 15:11
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    $\begingroup$ @Mithoron It is about matter, right? And there are ongoing chemical reactions, right? Then it must be the dark magic of chemists, the mages in white coats, gloves and googles, who understand all the mysteries of the matter, right? :-) // It seems to me physicists are more successful than chemists in delegation of part of their science out of their science. (chemistry is physics of interaction of atomic electrons) // In fact, it is a chemistry issue, but of applied chemistry within the battery technology, design and manufacture. Li-Ion/pol degradation has very interesting chemical aspect. $\endgroup$
    – Poutnik
    Oct 20, 2022 at 15:26
  • $\begingroup$ A very low charge could reduce the coulombic efficiency of the battery, specially the NiCd and NiMH. While a fast charge drop the CE to 90%, a very low charge could drop the CE to 70% $\endgroup$
    – Gui
    Oct 20, 2022 at 21:19
  • $\begingroup$ I just came across this paper. Table 3 shows a series of effects that contribute to degradation, and indicates whether they depend on low/high T, V, SoC, I. Many depend on high current, none on low current. Despite some noise here about CE without supporting references, all signs point to low current not being an issue. $\endgroup$
    – swineone
    Nov 18, 2022 at 5:29

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Low charging rates are issue only in cases if it affects proper detections of charge stopping thresholds. Typical case are NiMH cells, where signs saying to stop charging at C/10 or lower are not significant enough. Li-ion/pol cells have strictly given max voltage threshold which is easy to control.

Where it is applicable, like for Li-ion/pol laptops batteries, more important than the charging rate is the charge level management. Because, fully charged lithium cells have several times faster static aging than cells charged to 40-50%. And, near fully charged cells are much more sensitive to high temperature.

The typical scenario to be avoided is

  • high ambient temperature
  • device heated by high power load
  • battery being charged, with current charge > 70(80)% of its capacity.

Similar effect has the deepness of charging cycle. Shallow charging can provide within the cell lifetime 2-4 times larger total cumulative capacity, compared to full charge/discharge cycle.

E.g. in case the laptop is attached to AC most the time, and only occasionally running on battery, it is good to have charging start/stop thresholds near 50% of the charge capacity. E.g. 50% - 60%.

My experiance with Lenovo Thinkpads (T400/T430/T470/T14) is both Linux and Windows offer ways to manage it. ( Lenovo (commercial) Vantage for Windows, tpacpi-bat/acpi_call utils for Linux ).

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  • $\begingroup$ Thank you for this answer. Indeed I also watch out for heat and avoid high SoCs -- in a Mac this can be done automatically using e.g. the AlDente app. I concur that low C-rate charging is a tertiary concern. $\endgroup$
    – swineone
    Oct 20, 2022 at 14:27

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