I'm making a wearable project that involves me wiring up about 16 LEDs into a piece of clothing. Unfortunately, it's been many a year since I took a physics course and I'm a little rusty on things. Here's my situation: The LEDs drop about 2V each, and are meant to be used with a current of around 20 milliamps. I want to use a 9v battery as a power supply if possible. I used a calculator online (can't link to it because of low post count!) and it showed that I can do this by wiring a circuit that has 4 branches connected in parallel, with each branch containing 4 LEDs wired in series and a 56 ohm resistor. Assuming this is correct and won't explode me or anything, I have a few (likely ridiculous) questions: 1. I don't want to short out my battery, or turn myself into a fire hazard. What's the maximum amount of current I can safely be drawing? 2. When I've got things connected in parallel to the battery, how do I calculate how much current is drawn by this whole circuit? Do I add together the amount of current that each branch would draw? (And, er, how do I calculate that? I know V=IR, but I don't know how to get the numbers to plug into the equation...?) 3. I'm thinking my battery life might be pretty cruddy. To improve it should I reduce the number of LEDs hooked up to the battery? Is there a better power source to use that's still portable? Any assistance would be greatly appreciated. Thank you.