Ok I think I figured it out.
Using a precision 4.096 Vref to feed the adc & the dual opamp, MC34072.
Opamp A does a noninvering x3 gain to produce 12.288 VDC ref. which feeds the subtractin input of a difference amp, below.
OPamp B does a difference amp gain of x4 to produce a 4.096V output if the batt voltage is 1.024V higher than the 12.288. So the full scale adc at 4.096 Vref sees 4.096 V if the battery is at 13.312VDC.
This give best precision at 1mV = bit in a 10Bit adc.