How about using comparators to "digitalize" battery voltage ..
For exampe, the LM3900 has four of them in one body .. see picture below ..
Question is, do you need to convert 4-lines to 2-bits, or has your MCU enough available inputs to take 4 signals - up to you ..
You can add 1x7400 (4xNAND) and convert 4 outputs from 4 comparators to 2-bits .. see picture below .. or you can forget about all this stuff and employ one 8-pin PICAXE-8 microcontroller, which has 10-bit A/D and some general purpose I/O, and (first) perform A/D conversion and (second) translate result to 2-bit output ..
Mate, there are millions of ways of doing this .. just use your imagination !!!
I cant use an MCU , which woul dhave been the easiest choice as the current consumption would be much more as compared to the the comparators and the Nand gates.