From: Sean Breheny <shb7@cornell.edu>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Sun, 6 Sep 2020 11:10:56 -0700
Subject: Re: [OT] Simple LiPo charging circuit
Thread-Topic: [OT] Simple LiPo charging circuit
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I think your charging regime is indeed a very good one for longevity for
typical Li ion chemistry. As far as charging current I don't think it
matters much as long as the current doesn't warm up the battery much. As
temperature increases, the "calendar life" wear on the battery is
accelerated exponentially (see Arrhenius equation for a mathematical
model). So, the less time you spend hot (whether it is charging,
discharging, or idle) the better.

There are two kinds of "life" - calendar and cycle. Calendar life is
shortened by higher temperature and by high state of charge (for typical Li
ion chemistry - this is not true of most battery chemistries). Cycle life
is shortened by large changes in state of charge and maximized for making
cycles smaller (less change in SOC). This effect is not simply linear. In
other words, if you add up the total coulombs of charge which pass through
a 1 amp-hour battery in its life, then typically you might find that it is
able to to 1000 1 amp-hour cycles but is able to do 15000 0.1 AH cycles
(i.e., 50% better cycle life in terms of amp-hours).

Sean


On Sun, Sep 6, 2020 at 1:34 PM Bob Blick <bobblick@outlook.com> wrote:

> Hijacking the thread, I have a question about the battery in my mobile
> phone. I'm careful about charging, and want to get as many useful years o=
f
> life as possible out of the battery. I try to never let the battery get t=
oo
> low, never charge the phone if it's hot, and never let it charge fully.
> Based on the phone's gauge, I charge it when it's down to 40% and take it
> off charge when it reaches 80 or 85%. I think this is probably a pretty
> good way of doing it. I plug the charger into a timer so I don't have to
> watch it, I'm not totally OCD :)
>
> My question regards preferred charging current. The charger that came wit=
h
> the phone will do my normal charge regime in about 20 minutes. The good
> quality charger from a previous phone will take 90 minutes to do the same
> thing. Neither charger noticeably heats the phone.
>
> Which is easier on the battery, high current for a short period of time,
> or medium current for a longer time, both taking the battery from 40% to
> 80% state of charge?
>
> Thanks, Bob
>
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