My battery light has been turning on and off for about a week and the other day it barely started up after picking up my son from school so I went to my mechanic and he ran a test and the battery was getting plenty of charge so he told me that my battery wasnt holding a charge over night so I replaced battery under warranty and now after two days the warning light went on on my way to work do I need a new alternator?

 

Remove the battery saver https://www.f150forum.com/f38/disabl...-saver-425654/

How far are you driving each day?

Any aftermarket devices that could be draining it?

 

Batt light on.. alt.

 

I dont even get battery save mode . The light just pops up then goes away after a few miles. No aftermarket devices. I drive 10 miles round trip for work but been doing this drive for the life of truco.could it b a diode failing?

 

This

 

You should have your alternator checked. Once your vehicle is running you can put a multimeter to your battery posts, you should be seeing 13.5 - 15.5 volts. Most of my alternators I've had usually have about a 14.1v output. I use a ScanGauge II (which plugs into my OBD II port), and one of the "gauges" it can display is my voltage. So every time I drive I can see what my alternator is actually putting out. It can also display 3 other parameters of your choosing, as well as read trouble codes (DTCs), calculate fuel economy very accurately, and a few other things.

You can also bring your alternator to an auto-parts store and have them put it on their bench test.

 

Thanks for the replys I had them tested and they were 14.4 volt so he thought my battery was bad and so I replaced it under warranty and all ran fine for a day. Then today the battery light went back on

 

It's the alternator.. or a loose belt.. the voltage regulator in the alternator is going bad. Have it test under load to be sure.

 

Thanks. I hope it makes it till next mon or tues that's the only time I have to make it to the shop

 

I'd also consider parasitic draw while the vehicle is sitting with the engine off. There are a few threads on here with some common culprits on stock (unmodified) vehicles.

Make sure you check all your battery connections as well. Check for corrosion, clean them, and make sure they are tight. (Connections at battery posts, starter, and alternator for sure).

Oh, try and drive your truck a little further from time to time.