Alternator may not be working to keep battery charged properly.
Check with a voltmeter
Reading should be (with a fully charged battery) around 12.8 volts without vehicle running
With vehicle running reading should be 13.8-14.2 volts
Ford Focus 2001 - My experience with battery light coming on is the following: Put a volt meter on the battery if you get about 12.7 volts DC (Car Cold) or about 14.5 volts DC with the car running, your alternator should be fine. What you want too check is the fuse. In the fuse panel under the hood is a 10 amp fuse (red color) in position 10 (check your manual), if it is blown, that means your voltage monitor/regulator diagnostic module is suggesting it is not functioning. Replace the fuse should help. This also solved some stalling I had with the car, although I'm not sure why.
altinater is probobly dead
go to a auto parts store like advance auto and have them check your computer to see why it is on. they do this for free. this might give you a idea on why its on. if you havent already.
The battery light stays on when the alternator is over or under charging.
You can reset it with your OBD reader or you can disconnect the negative battery cable for a couple of minutes to reset the check engine light.
Most likely the problem is your alternator....the battery light actually does not monitor battery condition, only the charging system. I'd check the voltage regulator and the fuses first. The fuses are the cheapest fix and the voltage regulator will run about 25% less than an alternator.
First, you need to fix whatever's wrong, then you unhook your battery cable for about 30 minutes, then re-hook. If it comes back on, you have a problem that was not addressed.
Use a tester to see if the charging system is working properly. If your model has a separate regulator make sure it is working properly. Make sure that your battery is ok, a battery with an internal short can cause the charging light to stay on. The engine computer is the voltage regulator.
If the motor is rebuilt I think that maybe a sensor wasnt connected
I'm having the same problem. The cause of the nackered battery and dead alternator could be a faulty charge relay. Try replacing this and see if the light goes out..
Follow the positive cable from the battery, it will lead right to the starter.
Same as my 2002 P71. Battery had short. Replaced battery - worked perfect!
most 2000 model year focus have a fuel delivery module recall.