ubuntu-phone team mailing list archive

[Sam Bull <sam.hacking@xxxxxxxx>]

On Mon, 2017-01-16 at 12:38 +0100, Matthias Apitz wrote:
> El lunes, 16 de enero de 2017 11:43:16 (CET), Sam Bull 
> <sam.hacking@xxxxxxxx> escribió:
> > On Sat, 2017-01-14 at 14:49 +0100, Guillaume F wrote:
> > > (with the exception of my very first full discharge, 
> > > which went quite normally). So the hardware doesn't seem to be
> > > the 
> > > problem here and I probably can't be accused of mistreating my
> > > battery :).
> > Everything I've ever heard about Li-ion batteries suggests that a
> > full
> > discharge damages the battery and reduces its life expectancy. I've
> > seen recommendations not to allow the battery to go below 20%, and
> > other suggestions to aim to keep the battery in the range of 40-80%
> > (possibly with an occassional 100% charge).
> > 
> http://batteryuniversity.com/learn/article/how_to_prolong_lithium_bas
> ed_batteries
> 
> These tech pages does not support you suggestion. Ofc, one should not
> drain to really zero. The circuite must still be alive.

Thanks for the article, however this appears to mostly match my
suggestion, such as not performing a full discharge:

    The smaller the discharge (low DoD), the longer the battery will
    last. If at all possible, avoid full discharges and charge the
    battery more often between uses. Partial discharge on Li-ion is
    fine. There is no memory and the battery does not need periodic full
    discharge cycles to prolong life.

Following that is a DoD chart which suggests from a full charge,
discharging to only 50% will provide a 50% longer life span compared to
a 100% discharge.

Then:

    Most Li-ions charge to 4.20V/cell, and every reduction in peak
    charge voltage of 0.10V/cell is said to double the cycle life. For
    example, a lithium-ion cell charged to 4.20V/cell typically delivers
    300–500 cycles. If charged to only 4.10V/cell, the life can be
    prolonged to 600–1,000 cycles; 4.0V/cell should deliver 1,200–2,000
    and 3.90V/cell should provide 2,400–4,000 cycles.

Perhaps this is where the idea of not charging to 100% (e.g. charge to
80%) comes from. Though this appears to be talking about voltage of
charging rather than capacity, so you would presumably need a charger
which can switch voltages to make use of this.

    On the negative side, a lower peak charge voltage reduces the
    capacity the battery stores. As a simple guideline, every 70mV
    reduction in charge voltage lowers the overall capacity by 10
    percent. Applying the peak charge voltage on a subsequent charge
    will restore the full capacity.

Again, this might be where the occasionally charge to 100% comes from.

Again mentioned at the end:

    A laptop battery could be prolonged by lowering the charge voltage
    when connected to the AC grid. To make this feature user-friendly, a
    device should feature a “Long Life” mode that keeps the battery at
    4.05V/cell and offers a capacity of about 80 percent. One hour
    before traveling, the user requests the “Full Capacity” mode to
    bring the charge to 4.20V/cell.

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