It's difficult to explain without inorganic chemistry. Basically, all metals are just matter with "free floating electrons." That has to do with specific quantum properties I won't even begin to delve in to here.
There's a bit of a misconception here. Metals only lose their electrons when they form ionic bonds with non-metals. This is what happens when you make salt from sodium (metal) with chloride (a gas).
In a metal-metal bond, you're not losing electrons. Quite the opposite: you're gaining electrons in this system to stabilize it, and these valence electrons may move freely through the medium (this is why metal is ideal for making circuits and wires).
If you're interested in this, I'd suggest looking into the electrochemistry of batteries. This will make much more sense when you see it in a diagram.