Does it hurt anything? Some of the apps I use such as Garmin Navigator or some clocks keep the light on for hours at a time. I guess the backlight is an EL panel with a limited lifetime, but I don't know for sure. Does anyone here?

Well all light will fail. I don't know what the life of the light is. I know on Lap top the light ballast almost always goes bad way before the light bulb every dies.

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True, they do. Don't know if the BB uses a CFL though I suspect it does.

will it affect the battery life quickly?

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It will of course draw the battery down. But I use it on either an extended battery or power supply.