Unless you open a brand new package of new batteries, it is impossible to distinguish a full battery from an empty one.
You could of course buy a battery tester or you could use this simple trick that works every time and with all types: AAA, AA, C and D batteries.
If you drop the battery vertically, you'll know if it's still good: if the battery stays upright, it's full, but if it bounces before it falls to the side, it's empty or almost empty!
It is a matter of physics: the electric charge keeps the battery in a standing position and prevents it from falling to the side like an empty battery does.
See the demonstration in this video, you will soon want to try this trick to check the status of your batteries in 2 seconds! [Pub]
