If you always have two (or more) batteries at hand, you could wait until one is completely drained before putting in an other one. However, there's a big BUT here: working with an almost empty battery can cause your camera to malfunction... while you're transferring images to your computer, for example. This could lose you some valuable images..! Running out of power while formatting your storage card could even damage the card..! Bottomline: once you see that your battery is running (almost) empty, you better replace it or recharge it. It will probably shorten the battery's life, but it's safer that way...

We do not see things as they are. ǝɹɐ ǝʍ sɐ sƃuıɥʇ ǝǝs ǝʍ