Car stopped battery light on but battery new

It could be that the alternator stopped working or it could be something as simple as dirty battery cables. You said the battery is new and it's easy to assume that the cables were cleaned when the battery was installed, but I've seen many professional mechanics skip this simple step.

If you have a volt meter, you can check if your alternator is working. With the engine running, the battery should show at least 13 volts and it should not drop much if you turn on the headlamps and/or other electrical devices. If your voltage at the battery is low, check it at the B+ terminal on the alternator. If the voltage is OK at the alternator but not at the battery, then you have a cable problem between these.

Hope this helps,

BILL