What is the idle current draw of a charge indicator?

What is the most energy efficient charge indicator for a 12v battery? how many mW does it use for every state of charge?

• Start by asking yourself what measurement is necessary to indicate charge level of your battery and how precise do you need to be in this measurement. – Andy aka Oct 28 '18 at 10:14
• A very vague precision is fine, i.e. 4-5 LED's, 0.2v precision. – com.prehensible Oct 28 '18 at 12:52
• Pick any kind of indicator and have it powered through a push button. There are many charge estimation chips by benchmarq and others, they are intended to draw very little current. – KalleMP Oct 28 '18 at 18:04

$$P = VI = 12 \times 150\mu = 1.8\ \text{mW}$$