Battery light is usually on when you have a electrical problem. Usually the Alternator isn't charging. The brake light might be on if the brake fluid level is low in the master cylinder. Or it the brake light might be on cause the e-brake is on. Or it's a posibility the voltage has droped so much that it can't run some things if the alternator isn't charging.
[Edited by imcastock on Dec 30, 2005 7:28 PM]