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From: Martin Brown <'''newspam'''@nonad.co.uk>
Newsgroups: sci.electronics.design
Subject: Re: Battery (SLA) modeling
Date: Sat, 14 Dec 2024 17:23:02 +0000
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On 13/12/2024 17:23, john larkin wrote:
> On Thu, 12 Dec 2024 23:57:54 -0700, Don Y
> <blockedofcourse@foo.invalid> wrote:
> 
>> At a fixed time and temperature, is it safe to model a battery as a
>> fixed voltage source behind a series resistance?  Possibly, additionally,
>> a parallel RC to cover transients?
>>
>> In particular, does the model need to change based on whether the
>> battery is being charged or discharged?  (i.e., to estimate that
>> series resistance)
> 
> I've wondered about electro-chemical time lags, ions drifting around
> in liquids, as in what would the Spice model of some battery be? And
> on a slower time scale, the morphology of a battery changes with time.
> Nearly discharged batteries sure go Hi-Z.
> 
> What we need here is a good physical chemistry guy.

You can usually model them (voltage across real chemical battery 
systems) adequately with 2 or 3 different exponential decay time 
constants and amplitudes if you must.

The first is for transient behaviour ions already close to electrodes, 
the next for reactions already in progress in bulk and the very slowest 
for diffusion limited chemistry as the thing equilibrates into its new 
state. The latter can be quite long but usually only a small correction.

-- 
Martin Brown