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Hi,

so you want:

 V_ADC = (V_Bat - 40V) / 7.273

A lot of effort, ... just to gain a bit more than 1 LSB .. in ideal case.

The 40V is how accurate? The resistors have what tolerance?

Please do an error calculation.

I bet you gain almost nothing .. if not getting worse results. 

In my eyes it´s not worth the effort.

***

And then you talk about an 3.3V ADC input range.

This let´s me guess that you use VCC (3.3V) as the reference for the ADC. If so ... this reference may cause a more than 10 times bigger error than anything else.

VCC of 3.3V isn´t 3.3000 Volts. It has initial inaccuracy and drifts with time, with temperature, with load current. .. and usually contains a lot of noise.

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Again: please do an error analys of the whole system .. including VRef and even GND bounce.

This analysis shows where the biggest errors are. And you should start your (hardware) optimization at the biggest error sources.

Klaus