> numerous lead acid charger ICs on Digikey
> 
>    http://search.digikey.com/scripts/DkSearch/dksus.dll?Selection

That's Page 1 of 68,669 on resistors !! That's taking "from scratch"
a bit too far

> Has a good block diagram and discussion in the data sheet. Easily
> enough emulated in software and does most of what you want,
> probably

I've come across several charger ICs from the usual suspects and
downloaded their pdfs to get an idea of how they do what they do
with a view to applying the logic. As a PIC has all the elements
necessary to make a charge controller I was surprised that designs
seem a bit thin on the ground
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