Ok, A couple months ago My 2004 f150 wouldn't start, so I had Walmart to check battery,,said it was bad ,I seen it was bad on the print out they give. So,I bought the Big Battery they had like 1100 cca i think.. Was doing good till one night going home my low beams was flickering bad,,no Still no CEL at all..my scan gauge was going up to like 15v then down to 12v charging. I stopped at Advance to ck,, they said all was good. Well a month later woud'nt start this morning..Could Alt be bad ? checked wires ,seems good.Did it take this long to run battery down by just starting? Thanks

 

If your scangauge is showing a voltage swing of 15.0 - 12.0 Volts with the engine running, your alternator has lost its voltage regulation capability. As long as the voltage is above about 13.0 Volts, your battery is charging, so it may well have taken a long time to run the battery down.

But, there's one other problem. If the battery develops an internal short, that is possibly intermittent, you might see voltage swings like you describe.

Try recharging your battery to a full charge state using an external charger. DO NOT use the alternator to restore the charge, it's not built for this purpose. Have the battery load tested. If if passes, and the scangauge still shows the voltage swing, replace the alternator.

- Jack

 

ok tks ,,it does sound like a internal batt short Because at other times i looked at scan gauge it was at 14.1. So it can't be tested like it is?

 

The battery needs to be charged to be load tested. If you can't get the battery to take a charge, it tells you the battery is faulty without performing the test.

A charging voltage of 14.1 is right in the ideal range. If you see steady voltages between 13.6-14.2, depending on conditions, such as electrical demand, you probably have a good alternator.

- Jack

 

Well I had to work late, so I took Battery back to Walmart. He tested (I don't think it was load tested though) he said that it was almost 2 volts. He gave me another one . What made it so low? Should I get Alt. checked now before I put Battery back on. Are there a fuse somewhere to keep the charge going to battery? I never had a CEL

 

My honest feeling is, next time buy your battery somewhere other than Wal-Mart. Most of the batteries made in the US are made by Johnson Controls, as is WM's. Not ALL the batteries they make are created equal, but I don't think they make a very good battery. There should be a battery cable going directly from the alt. to the battery pos. post. I don't THINK there is any fuse in that line. An alternator needs juice to "excite" the fields for it to begin charging, unlike a generator, that's the reason there is juice to it all the time. When it starts, the same cable carries the juice to the battery (and actually on THROUGH the battery to whatever needs that juice). You'll likely need the new battery in for them to properly check the alternator. The battery is actually to start the vehicle and modulate the flow of juice, the alternator supplies the juice to run "all things electrical" on the vehicle.

With the vehicle shut off, disconnect the cable from the battery TO the alt. When you reconnect it, if you get a pretty sharp "crack" you know there is an internal problem with the alt. That may not throw a CEL, but that is not normal and indicates a constant drain, which should not be.

 

Which is best to do , take alt off and have it checked or leave it on ? All we have here is Auto Zone, Advance Auto, and Oreillys. Well I got the Battery back on tonight and it is charging 13.7 -13.9 while going to get gas with lights and radio on. I even unhooked the neg post while running and it never died. I am thinking I had a bad Battery now.

 

Sounds like it was something JC is good for, bad batteries. As an aside, I have heard that it is dangerous to remove the battery cable while running on newer vehicles because the spike can damage electronic components. I know this was a test in the somewhat distant past, but is now a no-no.

 

Oh I know,,,kinda just had to see if it would die,,Thanks for help !!

 

Read these captions:



You'd be amazed how many weird problems can occur just from that.