> I can offer some suggestions but need a tiny bit more information:
> what is the source of the charge current?

I'd supply an OTS plug-pack, 18V-ish DC, 1.5A. I might even make
the input more user-friendly with a bridge and buck-boost SMPS so
that any PSU in the general ballpark could be used

> In general terms, I usually charge batteries to their equalization voltage

That would be 14.4V ?

> then drop to float mode when the charge current falls below
> some low value

OK, current detection is one part I'd like to do with the PIC

So do you have a top-up period ? The diagram I referred to has three
stages - constant current to 14.4V, constant voltage (top-up) until the
current drops, and then float

> the charge voltage is temperature-compensated for the battery sitting
> under the hood as opposed to the temperature inside the automobile's
> interior.  In practice, I find that is not much of a problem at all.

I've not seen temperature monitoring mentioned for SLAs. Presumably
it's impractical because of their bulk and sealed nature

> Hope this helps!

Certainly does. Thanks 

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