Strange charging issue noticed after installing ALT-S fuse mod to cover AGM battery. Huge thanks to @4RunnerAquasport for the help so far but now its time to subject myself to 4Runner webMD diagnoses.

Replaced Battery today under warranty. Stock fuse shows the following. Pics are with the vehicle off, idle, and internal display idle voltage respectively.





When i installed the ALT-S fuse mod (from Dirty Parts), the internal display shows charging at ~14.2/14.3 volts. But the battery is showing 16 Volts at the terminals at idle. Thinking that cant be good, despite the mighty 4Runner operating without issue at those levels for a 20mi round trip at least.

Any ideas what can cause the disparity? Is 16v too high for an optima battery? Could the tune associated with being supercharged have changed something? Could it be the two amps drawing from the battery are causing the system to increase output? Also blew the 120amp fuse and a couple others last spring, (dealer replaced everything)

Lots of confusion happening at the moment. This isn't how i like spending my saturdays.

Your multi meter might be off. More investigation needed.

16V is definitely too high for any 12 volt lead acid battery, AGM or not. You are over charging your battery and that is why it failed and you had to replace it. The reason for the over voltage? Could be the fuse mod or the voltage regulator in the alternator. I would first remove the fuse mod and see what your voltages are. If they are still high, that would indicate the voltage regulator has been damaged.

The different voltage readings is probably due to the different places that are used for the indicators and probably not the meter itself.

This is after my truck idled a charge for 20 minutes, now at rest. Your meter may be off by a volt or more.

Attached Images

 

Could be

All voltages shown in the photos are with stock fuses. I’ll be getting a different meter on it this evening. My thoughts are I either have a faulty meter, or the voltage regulator was somehow damaged when I blew the 120a fuse. Reason I suspect the latter is because it shorted in the lead from the alternator cable to the fuse box. I had disconnected the battery but the cables came up and made contact and I didn’t catch it.

Problem solved, I have a bad meter, tried two others that showed a 1.5vt difference from the one I own.

Love this forum, Thanks for the help!

Cool!! I'm not right very often lol. It's good to know I have half a brain left.

I may be mistaken, but the meter shown in the opening post looks like the $5 variety available at Harbor Freight. I have a collection of those and have found they all read much higher than higher quality meters.
I sometimes carry one around in the vehicle I'm driving. While not accurate, they'll at least let me know if a circuit is dead.

How many of yall have done this ALT-S mod? is it worth it? it's only $5. What are the long term benefits? I first heard about this on another FB Page for the T9 stereo.

already many long discussions:

"Voltage Booster" for 31M AGM Battery

Is this dirtyparts replacement fused as well?

If not...I hope that circuit never exceeds 7.5A

Yes. It has a 7.5A fuse.

Yeah I’ve never really had to mess with circuits to this level of accuracy. I went full retard anyway and dropped $95 on a “good” one, at least it works, hopefully it’ll be used for more than just car mods haha