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Alternator charging ok in '07 Focus?

I have a '07 Focus and had to replace the Motorcraft battery recently because the car failed to start. Even the radio failed to start because it said ‘low battery’. I took the battery to Autozone so that they can test the battery and they said it had a bad cell. Got a Duralast battery and the car has been running ok for a month. The only thing I notice is that on a really hot day, I first turn on the AC and I hear a small tttt(maybe that is normal and just being paranoid)

When I put that other battery, the guy at Autozone did a load test where he had me crank up the AC and turn on my headlights. The voltage of the battery went down from 14v to 13.something(dont remember). He suggested I have the alternator checked because he says the alternator might not be charging correctly.

I then took it to Advance Auto Parts and they did a load test. The test revealed the Voltage went from 14.25V to 13.62V. The guy there said that is normal and that I should expect the voltage to go down a little. I also took it to a mechanic and they did a test too and they said its ok.

My question is it if the voltage going down to the 13.62V should be normal under a load test?

I’m taking the car for scheduled maintenance on Saturday to a Ford dealership and was probably going to mention about the alternator. Thanks.

It’s normal as long as the charging voltage goes back up to 14.25 after the load is removed. Voltage will drop somewhat especially when the headlights are on. The only load greater is the starter motor.

That’s perfectly normal. You don’t want to see the voltage drop below 13.5 volts with everything on. And once the voltage hits 12.6 or lower the charging system is no longer working.

Tester

The battery and charging system are normal.

The tttttt sound may or may not be. It could be the AC compressor clutch engaging, the fluid beginning to compress, or a physucal movement (of a refrigerant line or something) that occurs when the load of the AC compressor is felt by the engine.

Best approach: open the hood, stick your head under there (not too far), have a friend turn on the AC, and see what you can see. If everything looks normal dn the car and AC work properly, just turn the radio up.

I’m pretty sure you don’t have a problem. It sounds like they are just putting a voltmeter across the battery terminals and watching the voltage as you turn on things. Did you rev the engine with everything on? If it was just at idle, your alternator is very good. If you got 13.62 volts with everything on at idle, the voltage should have gone back up to the 14.5 volt range if you reved the engine to 2500 or higher.

If you have a gauge it should read about 14 while running, if you do not have a gauge a light should come on to tell you you have a problem.