2007 G35 Journey sedan. A few months ago the battery light came on and when I put a voltmeter on the battery with the car running it was at 11.9vdc so I suspected the alternator since I had recently replaced the battery. Got an alternator from a local rebuilder/reseller in San Antonio (a new Hitachi part, not rebuilt) and installed it and all was well for awhile. After about 3 months or so the battery light came on again with the same voltage reading. Thinking I got a faulty alternator I removed it and took it back to the vendor. They tested it and it looked fine with current up to 160A. I got to see them test it so no faking it. Put it back in and all was well, or so I thought. IIRC the voltage was in the 13.5 - 14vdc range. This was somewhere in the september timeframe. Since then the light has been coming on anywhere from every few weeks to a few days. It goes out after a few minutes of driving and starting is normal. I've had the battery tested, as well as the starting and charging systems, at an Autozone (where I purchased the battery) and nothing has been found. I know those systems are not the best diagnostic tools, but I haven't had time to get it to a shop. I suspect the battery since the voltage most times I've checked is around 12.63vdc which is typically low. Looking for anything else I can check before going to a shop and have them tell me it's the battery.

 

Look for a loose or corroded connection on the wiring. Take everything apart, use a wire brush to clean the lugs and the contact points on the equipment, apply a tiny thin layer of electrical anti-oxidation grease (buy a little packet from the parts houses, it's NOT the same as dielectric, you need anti-oxidation grease, DE-OX, NOALOX, or whatever they're calling it).

Also bend the wires around a little and look for damage on the insulation, bulging inside the insulation (corroded copper conductors), or anything else that doesn't look right.

An actual BATTERY SHOP will have a load bank tester (looks like a small welder mounted onto a cart with a heater and fan) for the battery to see if it's actually working, sometimes parts houses have them too but a digital multimeter is NOT how you test for a good battery.

It's still possible you have an intermittently failing voltage regulator in the alternator though, might have been defective but since the same problem exists before/after an alternator replacement it's likely a different problem.

When you clean up those battery cables you need to clean BOTH ENDS of each cable, I also strongly recommend cleaning the primary bonding jumper between the chassis and engine, remove the single 10mm bolt holding down the coolant reservoir, leave the hose attached, lift the reservoir up and there's a 2-hole lug under it that needs to be cleaned, the other end of that wire lands on the passenger side of the timing cover, clean that as well.

 

Got some time to do a little troubleshooting and found there is a 1A current draw with everything off. Some research suggests the "normal" draw shouldn't be more than 85mA. Guess the next step is start unplugging things to see where the draw is.

 

Start with the radio and CD changer.

 

So, I made a small mistake in my initial troubleshooting. I had a door open and therefore the interior lights were on which is why I was seeing a 1A draw. Took care of that issue, but I still have a 147mA draw until I remove the room light fuse then it drops to 80 - 87mA. I'll have to look through the wiring diagrams (Haynes manual, FSM's don't have this) to see what the culprit might be. For now I'll just go without the interior lights. Still, 147mA doesn't seem high enough to drop the battery voltage that much unless over a period of several days.

 

Yeah that's fine I have more than that (don't remember exactly how much) and my battery doesn't drain to no-crank unless the car sits for more than a week and a half, which it never does.

 

Yeah, the more I think about the more I'm sure that's normal. It hasn't ever drained to no start. I did find that the "room light" fuse also goes to the seat memory and seat controls. Anyway, have it on a battery minder so we'll see how it charges overnight and if I continue to have this issue. If so, then I'll have a more thorough check of the system done. Still leaning towards the battery.