It's charging. No, it's not. Wait, it is!! Nope.

[richardrichss]

I have a 1998 LX470 with a charging issue that ruined my day. After driving the car for a couple of hours, the battery light came on and the voltage dropped. This lasted for about twenty minutes then the voltage rose to normal and the light turned off. After about 30 minutes we repeated the process. It happens more often now, with the low voltage being pretty low. Now I have low voltage more often than not, wreaking havoc on my brand new Toyota battery. Terminals look good, cables look good as far as I can tell. Autozone tested the car while running and said the voltage regulator was bad and to change the alternator. Below are pictures that were taken literally minutes apart. I want to make sure I'm not missing something and that someone doesn't have a palm in face easy fix that I'm not missing before I tear things down. Thanks in advance.

 

[Spike555]

Bad alternator, when the voltage regulator gets hot it stops working, when it cools it works. This will continue until complete failure.

 

[gatormark91]

+1 on the bad alt. Battery light means it's toast.

 

[diego355]

Alternator x2.

 

[nissanh]

How many miles on the alternator? It could be the brushes which are about $16 at Camelbacktoyota (use OEM only). Try replacing it first. When brushes wornout the voltage can drop.
Part #6 here:
2000 Toyota Land Cruiser Parts - Camelback Toyota Parts - Genuine OEM Parts - Free Shipping