On Thu, 14 Sep 2017 23:22:06 +0100, "bm" wrote:

snip

My 2 x 16 LCD display will show the battery voltage, the current drawn
and the current Low Voltage Disconnect threshold from the magic
formula. The idea being I can get a sense of how long I can continue
to run at that speed (and I may be able to actually display that time
as early on in the battery discharge voltage curve it's a reasonably
straight line and that line *could* easily be plotted by me ITRW) ;-)

I reckon your flexicurve is the best/easiest idea.

It seem the only idea that I can cope with so far. ;-)

Bend it to suit what you have, bung the results into a look-up table and
interpolate between points.

Yup.

Even if you have a formula I doubt it will be accurate using real world
batteries.

You might be right but I'm not really expecting 'accurate' but a
reasonable guide. The thing is I could just go with / for a preset
'worst case' low voltage alarm value but I thought while I was
developing this Arduino based solution, why not see if I can make to
software do what it's good at?

Actually i'm unlucky with batteries even though i'm careful with them.

Ok?

I don't actually turn off the wipers when i go under a bridge but i'm
careful.

Yeah, that can be a big issue ... for electric cars ... ;-)

E.g, only sit at traffic lights using sidelights.

I've done that when 'nursing' a car or motorbike home that has a known
bad battery ... that and taking even more care to keep my foot off the
foot brake (1, 2, 3 or 6 (inc towing) 21W brake lights) and not having
indicators on (2 or 3 if towing) flashing 21W with a 50:50 duty cycle.

So, I'll keep looking to see if I can obtain any parallel information
from other manufacturers of similar capacity, chemistry and quality
batteries to help fill in the missing pieces.

Cheers, T i m