Fitted a new alternator in 2021 as the original was putting out voltage from 11 volts to 17 volts and with the new genuine alternator replacement, it read a constant 14.3 volts. New up-sized AGM fitted at that time as well.

Today was greeted by a message I've never seen before at start up, battery voltage low....

For the second day in a row upon startup, there's a horrific squeal for about a minute, definitely on the front right side with the bonnet open, could be the supercharger tensioner, pully or alternator. When it makes this sound, voltage output from the alternator drops from 14 volts to 9 volts until the squeal goes away. However, after driving for a while, alternator voltage has dropped to 13.6-13.8 volts.

EDIT: Both belts were replaced 2 months ago

 

Alternator voltage will vary depending on how full the battery is - the battery monitoring system controls it. The drop when the belt is squealing probably is just the belt slipping. Since its a relatively new belt, I’d guess it’s the tensioner or something got the belt and is causing it to slip. Could also be the idler pulley. There is a known issue with one of the idler pulleys going bad, which puts drag on the belt (and can actually shred it after a while according to a post on another forum).

 

Certainly could be the belt, it was new 2 months ago and has close to 5K miles on it now, so odd the noise would start now. Not certain what could have gotten on it, I've NEVER had any belt noise for the past 150K miles. Yes, slip will cause the alternator to not spin fast enough. Cant explain the sudden low battery voltage warning at start up, never have had the before...

 

So I've resumed using the CTEK and the alternator is back to 14.2 volts yet this morning I received the low battery voltage warning. Measured the battery voltage and it's at 11.9 volts so definitely a suspect battery. This's battery # 4 or 5, lost track, since 2016.
And here's the squeal, new dry belts and judging by the sound, it not a belt. Checked the supercharger tensioner with a stethoscope and nothing, moved to the accessory pulley behind it and I can hear the noise through it.

What do you think?

 

Yeah, doesn’t sound like a belt to me either. Not sure what that is. Wonder if you can just loosen that belt up and spin the idler pulley hand - see if it’s loose or gritty or noisy. No oil dripping on the alternator by chance? The alternator/battery situation is troublesome. New alt and battery in 2021 - that battery should still be good. I wonder if you have a parasitic drain. Maybe you can get that battery charged up (check it with a multimeter) and see if it holds a charge overnight.

 

Sprayed pulley with silicone, noise went away but replaced the pulley anyway. Old one seems ok, but there's just a very slight bit of grinding in the bearing compared to the new one. Drove to interstate battery and they ran their tests. It was a longish drive and of course the battery was at 12.9 volts. Digital tester passed, then they performed an analogue load test. CCA was 850, just as stated on the battery and voltage dropped to 10.6 volts under load which according to their tester is just at the edge of green so they said they could not replace it under warranty.

I checked current draw on the truck after it went to sleep and it measured .001 amps. Resting, battery started at 12.9 volts. An hour later, 12.7 volts, further hour later 12.5 volts and again another hour later 12.4 volts and now it reads 12.2 volts.

 

Battery dropped below 12 volts again, went back to Interstate and they gave me a new battery. Unfortunately the squealing sound returned today.

 

Realised I never updated this. Alternator died and fitted a new one, #3, June 2023. I believe that's now failing as well. If so, that'll be #4. And yes, all genuine JLR parts (Denso).

 

You almost got a year of it... meaning if it was done at the dealer... free replacement part and service.