Battery light usually means alternator not charging. Most common solutions would be be a bad alternator, bad connection, or loose alt belt.
Also check that the belt is routed correctly - I found a wrong way to route the belt and had similar symptoms.
See "Related Questions" below for routing diagram sources
Your charging system has failed, probably the alternator.
your alternator was never the problem. Its your battery and/or charging system. the reason the lights get brighter is because the car isn't getting the propper amount of energy from the battery and is having to directly draw off of the alternator. when the engine is rev'ed the alternator spins faster creating more current to charge the battery, witch is why the lights brighten at higher rpms.
With the engine running you should read from 13.5 to 15.3 volts at the battery with no lights or accessories on, with a nominal voltage at idle of 13.8 to 14.2, depending on temperature and battery state. Any less or more and the alternator is bad.
A bad alternator will have the effect of draining the battery, resulting in dim lights, trouble starting the car and the like. It would be best to replace the alternator as soon as possible and possibly obtain a new battery. This may vary depending on how much the bad alternator has drained it. You can get your alternator and battery checked any time at Auto Zone.
Sounds like you have something that is on all the time and drawing power from the battery. Check, dome, courtesy, trunk, hood, glove box, and brake lights.
There are several signs that an alternator is going bad. A few signs are dim lights, smell, warning lights, and a dead battery.
The engine is clicking with all of the interior lights on? Dead battery... and for future reference... if there is no clicking= really dead battery and it might not recharge. In that case check the alternator, if the alternator is still good, just buy a new battery. If the battery continues to fail to recharge get a new alternator.
check the battery and or alternator
I obviously means that there is something wrong with the alternator or battery. When both lights are on 80 percent of the time its the alternator. Either your belt fell off or your alternator went bad.
The diode in the alternator is probley going bad, Check charging system. And replace alternator.
Recheck your battery to see if hooked up right.
Weak battery? not holding a sufficient charge Alternator not charging battery sufficiently?