2010 FX35 Alternator or Battery?

[Who_Ryder1]

Hi guys, quick question. I have a 2010 Infiniti FX35 and I've been experiencing something strange. When I start the car (it doesn't happen every time), the battery warning light will stay on for about 5 minutes and then eventually go away. I ignored it at first, but today I started the car and it fired up normally, but both the battery light and BRAKE light stayed on for about 15 minutes before eventually going off.

I checked the battery voltage while this was happening and it was reading 11.57V. After about 15 minutes, the warning lights went off and the voltage was up to 13.9V. The battery is only about 18 months old. So, does this sound more like a bad battery, a failing alternator, or possibly something else? I'm especially wondering why the voltage starts so low and then eventually comes back up to normal.

I don't want to invest in an OEM part as I'm simply trying to keep this car until April next year. Any recommendations on AMAZON parts? I found this one.

Amazon.com: AISIN AFTERMARKET ALTN-00322 Alternator | Compatible with Nissan 370Z 09-10, 350Z 07-09, INFINITI G35 07-08, G37 08-10, M35 09-10, Q50 14-15 - V6 3.5L 3.7L : Automotive

Buy AISIN AFTERMARKET ALTN-00322 Alternator | Compatible with Nissan 370Z 09-10, 350Z 07-09, INFINITI G35 07-08, G37 08-10, M35 09-10, Q50 14-15 - V6 3.5L 3.7L: Alternators - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

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[teemoney]

Definitely sounds like alternator especially since the battery light doesn't come on for battery issues only alternator issues

 

[Blkinfi13]

I have had that issue a few times and realized it was happening when i was making more short trips as that was not enough for the alternator to charge the battery, i lost one battery that way, so whenever i drive 5-10 miles a week( total), i usually plug it into a trickle charger. Now for diagnosing ur issue -


1. Take it to an auto store and have them test it for you. I personally prefer to do it myself as i get better results with my multimeter.
its relatively simple to test it with a multimeter, if you have one and are comfortable using it, -- Steps below
Step-by-Step Testing Process

Step 1: Prep Multimeter
Turn your multimeter dial to DC Volts (indicated by a solid line above a dashed line next to V). Set the range to 20V (if your meter is not auto-ranging). Connect the red lead to the V/Ω jack and the black lead to COM.

Step 2: Test Resting Battery Voltage
With the engine and all accessories off, touch the red probe to the positive (+) battery terminal and the black probe to the negative (-) battery terminal.

Step 3: Test Cranking Voltage
Have a helper start the engine while you observe the multimeter display during the key turn.

Step 4: Test Alternator Output
With the engine idling, hold the probes on the battery terminals again. Read the voltage.

Step 5: Test Alternator Under Load
Turn on the headlights (high beams), AC fan on high, and rear defroster. Keep the engine idling and observe the voltage.

Interpreting Your Readings

Testing State	Multimeter Reading	What It Means
Resting (Engine Off)	12.6V – 12.8V	Battery is fully charged.
Resting (Engine Off)	12.0V – 12.4V	Battery is undercharged/discharged. Needs charging or replacing.
Cranking (Starting)	Stays above 9.6V	Battery has strong cold-cranking health.
Cranking (Starting)	Drops below 9.6V	Battery is weak, failing, or failing to hold a charge.
Running (No Load)	13.5V – 14.7V	Alternator is good. It is actively charging the battery.
Running (No Load)	Under 13.5V	Alternator is failing/bad. It is not producing sufficient charging voltage.
Running (Under Load)	Drops below 13.0V	Alternator voltage regulator is bad. It cannot maintain output under electrical load.
Running (Overcharging)	Exceeds 15.0V	Alternator voltage regulator is shorted. Overcharging will boil battery acid.

Quick Verification Check

• If resting voltage is low (< 12.2V), but running voltage is 14.2V: The alternator is working properly, but the battery is failing to hold a charge or needs an overnight bench charge.
• If resting voltage is 12.6V, but running voltage drops to 12.0V: The alternator is dead, and the engine is running strictly off remaining battery power.

Hope that helps
RR