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From: Bill Sloman <bill.sloman@ieee.org>
Newsgroups: sci.electronics.design
Subject: Re: Battery (SLA) modeling
Date: Fri, 13 Dec 2024 22:17:03 +1100
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On 13/12/2024 5:57 pm, Don Y 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?

The current carrying elements in a battery are ions moving through a 
soluvent, and they do look capacitative, but they are Warburg impedances 
and the capacitance varies with frequency.

https://pubs.rsc.org/en/content/articlehtml/2024/cp/d4cp00975d

> 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).

Probably not that much if the battery isn't getting close to full charge 
or total discharge.

Fully charged nickel cadmium batteries generate molecular oxygen at one 
electrode which diffuses back to the other electrode and oxidises metal 
there (which is why you can trickle charge Ni/Cd cells for ever if you 
keep the trickle charge current low enough). That might mess up the 
impedances a bit.

-- 
Bill Sloman, Sydney