Dual Battery Strategy

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TeCKis300 said:
While I do agree with rusty_tlc and jOnathN, do note that the output of the alternator is rpm dependent. So at idle, it won't charge the batteries at the same rate as if you were running on the highway.
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That's for sure. I can hear the solenoid in my dual batt system disconnect while at stop lights.

So you are saying Toyota had the forethought to design their alternators to be optimized for charging AGM and other gel cell battery technologies? Guess all the companies out there selling newer technology chargers for just that purpose are blowing smoke up everyone's ass?
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All sarcasm aside, the truth is somewhere in the middle. Odyssey recommends using an AC charging system on their AGM batteries every few months to top off the charge. It's been well documented by Slee and others that the stock charging system is not optimal for AGM batteries, and may contribue to Optima battery failures.

Slee said he's looking into an AGM charging system mod.

But on board battery chargers seem like they could be convenient but kind of overkill to do it every day.
 
I top off my Optima aux battery with a charger before I go on a major trip, specially if I load up
The fridge the night before. It is just extra battery capacity..
 
KlausVanWinkle said:
It's been well documented by Slee and others that the stock charging system is not optimal for AGM batteries, and may contribue to Optima battery failures
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Ding ding, this is what I was referring to. I was trying to find the old posts by Slee himself saying the same.

The alternator is NOT the best charger for the latest generation batteries, period. Sears has a specific charger for the Platinum batteries, Optima has a specific charger for their batteries now. No way the OEM alternator is designed the same.
 
Anthony.L said:
So you are saying Toyota had the forethought to design their alternators to be optimized for charging AGM and other gel cell battery technologies? Guess all the companies out there selling newer technology chargers for just that purpose are blowing smoke up everyone's ass?
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I've been running an AGM battery in my 1975 FJ40 for the last five years. The charging system may not be optimized but it seems to work pretty well. :meh:

Chargers are a different topic than alternators.
 
Anthony.L said:
Ding ding, this is what I was referring to. I was trying to find the old posts by Slee himself saying the same.

The alternator is NOT the best charger for the latest generation batteries, period. Sears has a specific charger for the Platinum batteries, Optima has a specific charger for their batteries now. No way the OEM alternator is designed the same.
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The charging system on the vehicle should dictate the type of battery used and not the other way around. To put a supposed incompatible AGM batt and jump through hoops with extra chargers, re-jiggered charging system etc., and get compromised life is completely backwards. But luckily that is not the case. In regards to specific standalone chargers, they are necessary because AGM vs. traditional lead acids have different voltage curves relative to charge state that the charger needs to understand.

That said, I don’t believe pre-mature failures are due to the charging system. AGM batteries are more tolerant to abuse, but can still be compromised. Deep cycling and constant parasitic loads will kill them just the same.

Which brings me back to my proposed strategy of a very large primary and small backup. For the same loads, a very large battery will not be cycled as deeply as a half size battery – and therefor maintaining better life. Of course you can go for two very large batts, but suffer the consequence of all the additional weight, packaging, and cost.
 
I am in the process of doing it (Dual batts with a 275 amp IronMan controller) via the very large primary, (31M) plus a good aux (34M) method. I plan to run all add on circuits to the AUX battery except for the winch.

There also are threads on here about squeezing two 34 sized optima's into the factory location.

Once my AHC fails, I plan to run two additional batteries, though one of those may go into the off-road expo trailer I am in the process of building out of a M101A2.

FWIW, I am using DH Platinum marine batteries (one installed right now) with a DH Platinum AGM charger hooked up once a month or so.
 
The bottom line is you are not hurting buy using an intelligent charger for your AGM batteries. I have not seen any issues yet with my AGM gp34 DH aux batt in conjunction with my gp27 lead acid. My gp 27 is due so is I'll be putting a gp 31 DH its place.

If you want serious discussions on this topic look to any of the sailing/boating forums.

AGM batteries are voltage sensitive and that's why the alternator may not be the best charger for them. They like a float charge of 13.5 volts. If your alternator is putting out more that can shorten the life of the AGM. The IBS controller I installed has a disconnect function if the float exceeds 13.5 volts. On the flip side if it discos the battery may not get charged. my Scangauge as well as my IBS controller generally report about 13.3 volts in the summer.

Sent from my iPad 2 using IH8MUD
 
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CappyKD said:
I am in the process of doing it (Dual batts with a 275 amp IronMan controller) via the very large primary, (31M) plus a good aux (34M) method. I plan to run all add on circuits to the AUX battery except for the winch.
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How do you like the Ironman kit so far? Looks like a nice setup, but I haven't seen anyone using it yet.
 
no-pistons said:
How do you like the Ironman kit so far? Looks like a nice setup, but I haven't seen anyone using it yet.
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Have not installed it yet, I'm still trying to get a mount fabbed to go behind my Ironman front bumper on the passenger side to hold the second battery.
 
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TeCKis300 said:
Which brings me back to my proposed strategy of a very large primary and small backup. For the same loads, a very large battery will not be cycled as deeply as a half size battery – and therefor maintaining better life.
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For the time being, what you describe above is my strategy. I have installed a Group 31M as the main battery, and feel like it's a bit of a waste if I don't take advantage of it to run more equipment.

My plan is to buy one of the carry-along stand alone jumper systems (after topping it off prior to a big trip.)

Perhaps something like:

Amazon.com: Clore Automotive JNC660 Jump-N-Carry 1,700 Peak Amp 12-Volt Jump Starter: Automotive

Does anyone have any recommendations on who makes the "best", portable jumper system that could fit this purpose?
 
Forging ahead slowly.

WP_000403.webp

Decided where I will be placing the backup battery and checked out fitment before I start fabbing a tray. I have a LX470 with AHC so note the AHC reservoir at the top that owners wanting dual batts complain about.

It's a Group 47 size battery. Pretty much the smallest that Costco offers. Fits pretty well. The small battery will work well for my strategy as it's completely a backup. So I don't want to pay a weight penalty or an overly troublesome fitment for a larger batt.

I will be moving 2 things to make enough room here:
1) Resister (pretty sure this is the daytime running light, DRL, resistor) You can see it moved to the bottom left of the batt hanging along the vertical wall.
2) The power steering reservoir will moved along side the battery. When I fab the tray, I make provisions for this to mount to.

I'll be making progress slowly as time allows so don't hold your breathe. But I will get pics once I fab up the tray.
WP_000403.webp
 
Last Saturday we installed the dual battery tray in my LX470.
It wasn't that hard, only thing was to find the right length of hose from the power steering reservoir to the pump.
It is the Piranha tray and it should hold a full size battery.
 
Tell me more Wil. Got links to that tray and pics of your install?

This definitely is not hard. I'm just documenting my take on it. And I'm not new to these type of things having self built and tuned a 400hp Lexus in my own garage that I daily drive. I enjoy the satisfaction of fabricating/building stuff myself.
 
Pictures are not that good.
In Australia the V8s have a cyclonic air cleaner, sorry.
 
We call it a dual battery system so I bought a dual battery tray.

Hey, I am living in Oz country and have tyres, not tires. :-)
 
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