What does it mean when the brake light and battery light come on?
Considering this, why would battery light and brake light come on at same time?
Incidentally, the battery and brake lights are the same lights that come on when the key is turned on and the engine isn't running, which would indicate an alternator problem, as the alternator isn't turning at this point.
Keeping this in consideration, what is wrong when battery light comes on?
The battery light indicates a battery charging problem. If the battery light comes on and stays on while you are driving, the most common cause is a broken alternator belt. Total failure of the alternator is another possibility.
When the battery is very weak, this may inadvertently cause other warning lights to come on, such as the ABS light as a result of low battery voltage. When the alternator is not working properly, this may result in the battery quickly losing charge and the car losing all power.