Hi there, My battery light does this odd thing...

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Hi there, My battery light does this odd thing... It flashes on and off before I start my van. I put the key in the ignition and turn it to the point just before the starter engages and the battery light either flashes on and off or it does not come on at all... if it does not come on at all my volt meter on the dash reads about 9 or 10 volts. If I try to drive the van will die. If I step on the gas, still in park, the volt meter will rise back up to 13 to 14 volts and stay there and the van drives normally. Any idea what's going on?? ss