The battery temperature sensing may need to be remote, therefore using i2c may not be such a good idea (distance , protection, number of wires). Dallas (maxim) have a 1wire temperature sensor that requires 2 wires (1wire actually needs two wires!). You can get a variety of micros with on board a/d converter for probably less than the cost of an adc080x. Philips have their LPC932 series of devices.