Just an update in my case.

I seem to have a parasitic draw that pulls about 180ma, and though my AGM can go deep I need to leave my Arclight Booster at Max boost for the full ~14.9V charging in combo with the occasional slow recharge. Had been doing fine till I can get to the dealer to figure out exactly what the draw is.

However at -5 degrees on my way to work after warming up the 4R I was getting wide voltage swings from 13.6v to 15-17v which is bad, short bursts but still worrisome none the less as well as some dash light warnings (Very brief).

Thinking max boost is fine in colder temps but if its going to get super cold maybe do regular boost.....

The diode is rated at 1 amp vs the stock fuse (7.5a)

I ended up removing the diode ansrer taking some readings at cold start, driving and idling after warmed up

Posted in my build thread:
Octanejunkie's T4R project - 99 SR5 4WD 5-speed

I get wildly different voltage ranges with or without the booster and depending on boost level. Stock has never given me more than 13.9.

Older 4 runner?

99 SR5 with stock alt, assuming 80 amp

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I realize this is an older post. Was about to do the GM diode with a fuse mod on my 2006 4Runner bought the parts decided to run some tests before mod. But now having doubts. I’m getting 14.0v at alt. And my Odyssey battery 34R says float charge at 13.5-13.8. Cycle charge 14.4-14.8. Running at cycle charge will shorten lifespan of battery according to Odyssey and everything else I read. I do have quite a bit of draw on my system, 1.600 watts stereo, light bar with 4 additional light and a bunch of other mods. My alt probably has less than 10k on it.

I was going to do the add a fuse with the fuse and diode, not about to run a straight diode.

Now I may have messed this up by charging my battery the previous day. I’m taking readings directly off the alt and the battery both for comparison. But yeah a charged battery will affect the reading off the alt. I tried running it down with about everything on. Was able to get it to drop to the 14.0 at alt and 13.8 at battery after running it for a while.

Any thoughts or suggestions?

You probably have less load than you think you have. A "1600 watt" stereo does not consume 1600 watts all the time, but only during very brief periods at peaks of the music, assuming you have the volume turned up to ear splitting levels. (Most people with high power stereos will put a large capacitor, 1 Farad or more, on the supply line to provide the extra power needed for those peaks.)

Most added lights now days are usually LED, which draw significantly less current than halogen lights, perhaps only 1/10 of the current.

All your voltages sound normal. No worry there. What is the current out of the alternator when everything is on? That will tell you the actual power (watts) you are using.

What is the battery voltage with the engine off, no load? Should be 12.3 to 12.6 volts. If that drops significantly, it would indicate a battery that is starting to go bad.

Battery is about 12.5 and I just checked it’s 5 years old. My lights are halogen and HID‘s. Bunch of old school stuff mods I did years back. I realize the stereo stuff is in short burst.
Really should have done more long term testing. When I turned everything on yesterday it went to 13.9 on alt and was dropping. I should’ve held it longer than I did. I got the parts ready to add the diode but just was thinking maybe I don’t want to overcharge it.
Over the years I have had to replace the alt at about 100k miles and battery’s seem to make it 6 years. But I was also harder on it and a lower output charger. I have since improved on all things.
So really at 5 years and 12.5v that’s pretty good from my understanding that’s about 80%
I’ll test again and run things longer. Just mainly concerned about overcharging it.
I should add I have 4 halogen lights, and a lot of LED mods. Rock lites, floor etc…running 0 gauge from battery to almost right tail light. Have my amps hidden in the back panel.
I used to have dimming headlights, I should have know because it was going on for a year before my alt went out.

I’m probably overthinking all of this. Here’s a quote from Odyssey.

“One other thing to note here, and this applies to any day of the year, is that some alternators may not have the ability to keep an AGM battery fully charged, especially if you only drive short trips. It is always a good idea to have a maintenance charger to periodically boost your battery to 100%, that way it isn’t so critical when the car is not being used for several weeks or months at a time. Some aftermarket high performance alternators are also available that can help with this problem.”

So my 4Runner does sit for days at a time. Also lots and lots of short trips. I’m at 112K miles on a 2006 and it had 75K in 2011.
38K in 13 years

I do put it on a charger every so often especially if it’s sat around for 4-7 days etc..