how do I determine how long a battery will last in a simple circuit?

Question

Given 6 white LEDs wired in parallel, each with forward voltage of 3.3v and drawing 20mA, using (3) 150 ohm/0.25W resistors, how long before a typical 9v battery dies? How do I determine this in the future?

FWIW, the schematic I'm using is the one created by the LED wizard at: led.linear1.org/led.wiz .

+----|>|----|>|---/\/\/----+
+----|>|----|>|---/\/\/----+
+----|>|----|>|---/\/\/----+

This shows 2 LEDs + 1 resistor connected in series as a group. Each group is then connected in parallel with one another.

My goal is to light this array to in a way that it is optimized for brightness and long battery life. The choice of 9v power source isn't a requirement: 1.5v AAAs/C/D cells connected in series is also legitimate.

Answer 1

on batteries is notated stored energy in Ah. 9V batteries have around 300-500Ah (200Ah or less for accumulators).
the stored energy: 9V*300Ah= 2700Wh

1.5V batteries/ accumulators have much higher values e.g. 2500Ah, 4500Ah depending on its size and type

so if you have 300Ah and you draw 60mA => 5000h

Answer 2

The ampere hour capacity of a battery varies with the amount of current being drawn. Figure the total current you will flow and contact a battery manufacturer to find out what they say. They might not have a number for your exact current, but probably can bracket it with past results so you can extrapolate an answer.

Answer 3

taking into interest the very incontrovertible reality that a battery makes use of pink cable for the effective terminal (+) and black for the unfavourable (-) I reckon the corporation deliberately protected those 2 cables for ease of use and id. can't quite say extra as you haven't given any specification for the unit besides the undeniable fact that it would want to properly be common adequate.