I see that a few outfits offer "Alternator Voltage Boosters" or the like, that go in the engine bay fuse/ relay box. Apparently this can up the alternator output voltage by .60-.80 which might be better for AGM batteries.

It seems that these are a diode or resistor housed in an add-a-circuit.

I have the Diehard 31M AGM battery and tray in my 2014. For the past year or so I was driving upward of 500-1000 miles a week. Now my driving consists of around town and occasional weekend getaways. I am finding that I need to charge the AGM 31M manually.

I also have a dual battery setup, but it disconnected until I get things sorted out.

Yes, I know that these things are snake oil and will blow up my alternator. My question is why are these bad. Heat?

sounds interesting, happen to have a link? thanks

pete

Can't help you there but I would propose it may be cheaper/easier/better for things to make up an excuse to drive around for an hour or so each week to charge the system and get everything else warm/lubed up?

Edit: How often are you having to charge manually and how are you making the call do so? Voltage meter? When the truck wont start?

Well... the (AGM) battery would probably be the only thing not affected (Though if you put a non-agm battery in or your second battery is non-agm then that'll be the first thing ruined.)

It's everything else in the car, all the electronics etc. Pushing the V on everything a bit... could have repercussions at some point.

Someone has to be a test subject!

For now I'm content with externally doing a desulfation charge cycle on my AGM battery a couple times a year and hoping that gets me a decent life out of it

Sure, here you go.

Or here.

There are some others as well if you search eBay or google.

I've got $10 that says it "boosts" voltage by cutting the amps.

@Engineer Thanks. I may be just making a problem that doesn't exist. I tend to throw it on the charger every two weeks or so. I tend to notice when it doesn't have the same cranking pep as normal. It is driven daily. Not as bad now that it is warmer.

@2014 Warthog The other battery is an AGM as well. I guess I just feel that the system isn't charging as well as I had hoped for use with two batteries, lighting, fridge, winch, etc.

Well actually the main problem is that the stock alternator is only BARELY able to supply the AMPS necessary to drive the car let alone charge two big batteries :/ Higher voltage would help push spare amps into the batteries a bit better but there are precious few spare amps even available.

I've been wanting to install a beefier alternator for that reason. At idle, the alternator output fluctuates right on the hairy edge of "ok" on the charge meter I have.

The main issue is that it is ridiculously difficult to change the alternator out in the 5th gen and finding one and rewiring it into the system is a tad scary to me as well

In the old days it would have been SO easy! But now with the computers and all the other electronics... it could be an expensive game upgrading the charging system. :/

First one looks like fake and probably doesn't do anything

The other one appears to have a standard potentiometer (adjustable resistor) I assume to trick the voltage regulator

I recently performed a dual battery setup after a ton or research. I used a FET battery isolator. Even with it's very small voltage drop, it has an smart alternator sense line to keep the alternator internal voltage regulation working through off/starting/running, even with the LE push button start. Still, with an AGM battery, I was thinking of doing something like this. The float voltage is within range, maybe on the low side, assuming ambient temp at the time. I wouldn't be surprised if the vehicle compensates for temperature, like my $50 1500 mA charger does, but haven't tested across various temps yet.

I haven't looked into how to compensate voltage for AGM yet and can't say whether a passive resister would be sufficient. There is a 7.5 A alternator sense fuse, and the line comes out a connector on the lower passenger side of the fuse box. So, at first glance, they look like they could be legit.

I'm not an electrical engineer, but close, and run ideas buy them all the time.

Bottom line, the difference in charge voltage on an AGM is something like 0.1 or 0.2 V. With a 5 year warranty on the X2, I'm more worried about the Texas heat killing it in 6 or 7 years.

Second the alternator upgrade if you plan on pulling some juice from your battery and not going to drive all day or plugin in to charge it. Check out the 270XP. If I wear mine out or or am needing more charge, I guess I'll pony up for it. It should be a direct replacement. I'd replace the cable with 0 AWG though. In the meantime, periodic manual charging doesn't sound that bad. In fact, I just used a desulfator to revive a dead backup battery starter, so I don't mind the idea.

4Runner alternator upgrade (gen 5)

Thanks for the info. That is partly how all of this came about. I had the National Luna isolator system and found that it wasn't charging either AGM battery as well as I had hoped. Not to even mention idle or accessories. I have another system with a HO alternator that is running the Hellroaring solid state isolator. I am swapping the two systems hoping the solid state unit will be more sensitive to the voltages.

As for the booster gizmo. It sounds like it is a diode placed in the sense circuit to create a voltage drop, increasing output by a bit. A bunch more info on the Prado forums, here's a another good link , and here is a FAQ of the guy that came up with the whole thing.

So who wants to be the Guinea Pig and pay $40+ for a fuse with a $2 diode inside?

Back to that HO Alternator and pulley thread.........

I just tested. My alt is putting out 13.7+, the max float charge according to the X2 battery label is 13.8. Resting battery voltage is 12.8+, considered 100% SoC. Installed 5 days ago. I would have offered to play with the return voltage, but I don't have any margin to do so.

I wouldn't be surprised if the solid state isolator has more of a voltage drop and makes your problem worse. I'm all for true isolation like solid state units do but that is another story.

What is the voltage across your battery terminals with the vehicle off? Idle? 2000 RPM? Are you powering any kind of load when not running or extra load when running?

I have 2006 4Runner with the 4L running a Dc Power Engineering 270xp alt, northstar 27f agm up front and 2 Northstar asm220agm batts in back powering 2 Sundown Audio SCV-6k's and am having the dreaded Toyota crappy voltage warm issues of 13.4 once it is hot. Have tried both of those modules you listed and for some reason neither of them work. The Dirty Parts one had a cold start voltage of 14 which is what this truck has always been so no change there but the battery light was on as soon as i put the bypass in the fuse. The Mechman part didnt even turn the alt on at all and yes the excite wire was on the alt positive post. Just a warning to everyone running aftermarket alts. These Products may or may not work on your application. Mechman claims theirs to work on stock alts and their alts but no guarantee on other after after market units. The Dc Power Alt uses a Stock Denso regulator so not quite sure what the issue is but i have now spent close to $200 in parts that do nothing and are paper weights essentially.
Figured i would let everyone know my experiences so they can draw their own conclusion and make their own decisions on what they buy.
Next option will be a dual voltage MLA unit from missing link audio and pray.

I have been an auto mechanic for 20+ years so this is starting to get rather frustrating that we cant find a product that works in a given scenario.

Good Luck Everyone.
Chris Carter
Midwest SPL Competitor
Usaci Street Beat 1 Competitor.

Now I know that I'm missing something... (Please help!)

I've been following this thread but have yet to hear anyone discuss the 'Checks and balances' of FIXED load and recovery in an auto electrical system. This works much the same way as an individual who may be on a fixed income. My fixed load is the calculated electrical accessories that I have installed in my rig. And the fixed recovery represents the safe maximum current that I can generate to maintain the accessories that I've enjoyed using in the truck, and the amount of current (amperes) that the alternator was specifically selected and installed because it has the capacity to safely generate enough amperage to supply the electrical system's fixed load, and still has plenty current left over to develop the output needed to charge the battery(s) without ever needing to 'Full-field it's rotor; a condition that exists when the alternator's components aren't large enough to meet the electrical demands without over extending the maximum output rating of it's copper windings, diodes, and (forced air-convection) cooling system.

So if/when the alternator is not able to keep up with the MAXIMUM running load of the vehicle (regarding amperage), the available alternator voltage output will begin to decrease to the point where it's no longer able to maintain even a 12 volt battery voltage. Once this happens, it's 'GAME-OVER'! My question is: "Why aren't we now trying to determine what the REAL trouble is?" If the alternator isn't charging the battery(s), there's a reason. Either our 'fixed' accessory load is much too high for the alternator's pre-determined S.M.O.C. (Safe Maximum Output Current) to where there is a serious voltage sag in our vehicle's electrical system, or, our selected alternator may need to have it's safe maximum output current re-evaluated. You understand that I'm trying to learn this very different approach to an undercharging electrical system so perhaps one of the experts here can help me to get on-board with the rest of the team!

rig