On Sun, 17 Sep 2017 13:26:32 +0100, John Rumm
wrote:

snip

I can see that working where your source data are following some kind of
exponential change being driven by a single (or predominate) physical
variable, but it can get rather complicated where you have multiple non
linearities competing in the same data set that have different
weightings at different times in the process. You may find you just end
up setting yourself a task that is of equal or greater difficulty to the
original question.

You may be right John but I was just hoping that 'maths' would be able
to cope with it, no matter how inaccurate the result might be ITRW.

If you are starting with an empirically collected data set, then you may
find that after manually fitting a line (flexi curve etc) you can
identify sections that behave differently from others, and then attempt
to model them separately.

Looking at the graphs I have seen that represent what I think I'm
looking for, the range of currents I'd be dealing with seem to be in a
reasonably 'linear' (as in say 'exponential') area.

If you look at the graph labeled 'Discharge characteristics at various
currents' he

https://www.thesafetycentre.co.uk/doc/583.pdf

and consider the 2-10A range (= 0.33 to 0.05C when seen across the 3 x
~30Ah batteries in parallel as that battery is of a similar capacity
to one of mine) then it doesn't look like there should be anything
unpredictable.

Even if we only considered it as a straight line, couldn't we
'compute' the (say) 50% DOD cutoff voltage for any current within that
range?

Cheers, T i m