Something is usually on that you don't know about like an alarm could be draining the battery. However, If its not starting you should check the starter though. It will make you think the battery is bone dead.
i think you are having problem with your alternator its not charging your battery
Alternator not working properly or not connected properly. Wherever you bought the alternator take it back and have them check to make sure it works properly. Also make sure the new battery was fully charged when you received it. HTH.
the common cause why the light is on is that your alternator is not working well,try to have your alternator checked .may be the carbon brush is already worn out.
I just put a new battery and alternator in my car, but when i put it in gear or start slowing down to stop..the car die out. Also the brake light is continely on.
alternator is probably not charging. you need to fix this NOW. new alternator is likely the only repair.
its the alternator if the car is running with a battery light on. but check fuses first
Repair the alternator to battery connections or replace the battery.
The the alternator is defective.
maybe you need a new alternator
Voltage regulator or loose wire.
Your alternator is probably rebuilt and not really new. I have had this problem several times and I have bought a new battery and alternator. The alternator keeps your battery charged and powers your electrical system, so even when driving you can lose all power in the car from the alternator draining your battery. Take the battery and alternator to an auto store and they will test both for free. Ask them about the difference in a rebuilt alternator and a brand new one. This is a very common problem.
Only if the old battery is defective