Re: Battery (SLA) modeling

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.
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Bill Sloman, Sydney