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From: Don Y <blockedofcourse@foo.invalid>
Newsgroups: sci.electronics.design
Subject: Re: Battery (SLA) modeling
Date: Fri, 13 Dec 2024 17:06:40 -0700
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On 12/13/2024 4:20 PM, ehsjr wrote:
> On 12/13/2024 1:57 AM, 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?
>>
>> 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)
> 
> For what value of "safe"?
> 
> Probably better, in general, to use manufacturer's
> discharge curve, at least as a starting point. If
> your application differs appreciably from the test
> conditions in the manufacturers specs, you need to
> test it yourself, again depending on what you have
> in mind by "safe".

Discharge curve depends on knowing the starting point SoC.
For a battery in continuous, cyclic use, you need to
*determine* the SoC at any given time.  I.e., when to
STOP charging, when to stop DIScharging, how much charge
you can expect to have available, how long until you
are likely going to reach "full" charge, etc.

> It's better to design the system to accommodate the
> battery at its best and worst SOC/capacity levels.
> Also the age of the battery and how it has been
> treated over that age is a factor, so take that
> into account too.

The hope is that by continuously updating the (albeit
simple) model, you can reflect the effects of age IN
the model and, potentially, indicate when replacement
is required (which largely depends on the service it
has seen)