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Why do I need 2 3V batteries (to power 2 LEDs) and how come 3V coin type batteries come in so many different sizes? Answered

I'm following some instructions and the materials list says I need 2 3V batteries and a twin battery holder. I can't find a twin battery holder so I'm just wondering why I need 2 batteries and also why there are several different sizes.

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The 2 LEDs are in series, I don't now about the batteries. This is supposed to be for people with no prior knowledge but its really hard to understand :-s

3V batteries? Are you sure they're not two 1.5V batteries?

L

not really....

they just have a different battery chemistry:
http://www.dealextreme.com/details.dx/sku.6999

I meant that they're not as easy to find as lower voltage cells, guessing that 2 x 1.5 = 3.

L

Depends on your LEDs. The colour affects the forward voltage - if you have 4V LEDs, 1, 3V battery won't work.