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Hi Guys, ( I am prickly)

I am really excited as I'm going to make my first project ever that includes resistors. I needed some help regarding (no not resistors) batteries. I need to chose which battery to use either 2 AA batteries (3 LED's in parallel)  or a 9v battery  (3 LED's in series). I want to choose the way in which the LED's will be brighter for longer.

-Prickly Potato

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That's not a dumb question, one of the smarter ones relatively speaking. Battery capacity can become a bit tricky, but keeping it simple; Watt-Hours is the measure of energy stored. 1WH means 1 Watt of power delivered for 1 hour. 2WH would mean either 2 watts delivered for an hour, or 1 watt delivered for 2 hours. (in other words, it is the product of the two: WH=W*H )

I am sure you know that to get watts, you can multiply volts (electrical pressure) and amps (the flow rate for charged things, like electrons.) If not, then watch this:

As you get more advanced, you will see that batteries are weird in that the voltage is not constant as the battery dies, so it is not as simple as "exactly one watt for 4 hours, then zipiddi-dohh-daa" because when volts go down over time, generally, so does current (amps) and power will definitely goes down*, then the battery dies away slower and slower, your LEDs fade, motors slow down, (usually drops kinda quickly.) and you get a nice curve, called the battery discharge graph. (look it up, pretty interesting!) https://www.google.com/search?q=battery+discharge+...

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You can then calculate total energy stored in the battery by taking the graph and figuring out the area inside it. like if the curve was a perfect square, W*H is like figuring out the area of a rectangle!!! Hope that makes sense! but anyway:

There are some great tutorials online that cover the basic, easy calculations for battery capacity (Watt hours (WH), joules, etc) and charge (Amp hours (AH), Coulombs, etc.)

(Sorry that is pretty long, I hope it all made sense!)

it swamped me.

You'll get much longer life from AA than a 9V