So it seems when the engine is cold (like first.

So it seems when the engine is cold (like first start this morning) My battery light comes on and my battery gauge is very low immediately and I put it into reverse and it sputtered almost as if the car was going to die, So I stomped on the gas and the sputtering seemed to stop for the moment, But when given no gas it just dies completely. I let it sit in idle for a very long time and I was tinkering around under the hood, went back to the driver seat and the battery light was off and battery gauge was back up to were it normally is. Took it for a test drive and seemed to do just fine. Turned the ignition off and started it back up and no lights were on and battery gauge was normal. So it seems to run fine when the engine is hot. But dont know whats wrong, Can you help?