Why IS my 2007 Lexus es350 battery light on?

If the battery light comes on in Your 2007 Lexus ES350, it's indicating an issue with the charging system. This could be because the terminals on Your battery have corroded, or the cables have become compromised. There could be an issue with the alternator, which is also a very common reason for this. Then, there's the serpentine belt, fuses, and the battery itself, all of which issues with will result in this light coming on. If You've visually inspected the terminals and cables, and checked the fuses, the neXTStep is to verify the voltage on the alternator. You should see between 12.5 and 12.8 volts on it. If You're getting below that, the alternator's definitely suspect; try charging the battery and checking again before deciding for sure it's that.