How to trickle charge a dual battery setup?

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

FDNewbie

FDNewbie

10 Year 15 Year
Joined
Feb 21, 2008
Threads
53
Messages
457
Location
Tampa, FL
I have a dual battery setup done by Iron Pig Offroad in Fredericksburg, VA (who do *awesome* work, btw). I typically leave my cars on a trickle charger, because I don't drive them very often. But I noticed something ever since I had the dual setup done; trickle charging with the dual battery doesn't "work" as it typically should.

- If I place the charger on the primary (starting) battery, it takes FOREVER to reach full - and I mean like 3 days. Even a completely dead battery typically fully charges in 24 hrs.

- If I place the charger on the secondary (accessories, winch, etc) battery, it'll charge, but when it's done, the charger will give an error code.

Both batteries are NEW. Basically I think having both batteries on a single circuit prevents the trickle charger from working as it normally would.

I know the simple answer is just to remove the positive terminal from the battery I wanna trickle charge and then place the charger on it, but:

A) That's a PITA to do every time, vs. simply removing the charger and you're ready to drive.

B) Removing the positive terminal from the primary battery means I gotta reset all my presets (radio, clock, etc) all over again, each time.

Wondering if anyone else has any ideas/insight on another simple way to make this work.

TIA!
 
What trickle charger are you using?

I highly recommend a Battery Tender brand unit, it will charge and then maintain the battery at a float voltage, versus charging and charging and .....

How are the dual batteries wired up, i.e. what joins/separates them when running/stationary?

cheers,
george.
 
When connected to the starter battery it may be charging both batts. Iron man is a voltage sensing relay iirc so the trickle charger would connect both batts. Thats why its taking so long prob.
 
george_tlc said:
What trickle charger are you using?

I highly recommend a Battery Tender brand unit, it will charge and then maintain the battery at a float voltage, versus charging and charging and .....
Click to expand...
Yep I gotcha. This is the unit I have: Battery Manager IV - Battery Care - Car Maintenance - Griot's Garage. It'll charge without overcharging. Pretty nice unit IMO.

How are the dual batteries wired up, i.e. what joins/separates them when running/stationary?
Click to expand...
Here's the info they have posted on their website: FZJ80 Dual Battery Kit [IPOR-FJ80DUALBATT] - $499.95 : Iron Pig Off Road, Toyota Land Cruiser experts, including the detailed install instructions, so you can know exactly how it's setup.
 
On my dual batter set up with a voltage sensing solenoid, i have to separate the batteries and charge one at a time or else the solenoid will open and close due to it sensing the 12+ voltage ( whatever the amount of voltage it is to close solenoid and connect the batteries) the with a battery tender.
 
Yeah, with an auto sensing solenoid based unit I'd say you're going to have problems, especially iwhen it engages a solenoid that will draw current. The charger will be trying to top off the current being drawn by the solenoid....

I'm very happy with my 'dumb' dual battery setup, no current is drawn if the alternator is not running. I can manually combine the two batteries and top them both up at the same time or separate them and use a tender per battery.

cheers,
george.
 
Well, the URL just shows a picture of a control unit with a solenoid. I assume it is just wired to the batteries, so if that is the case and there's no dedicated lead going to the Alternator Good signal, then it'll be autosensing. What's the actual part number and make of the isolator?

cheers,
george.
 
george_tlc said:
Well, the URL just shows a picture of a control unit with a solenoid. I assume it is just wired to the batteries, so if that is the case and there's no dedicated lead going to the Alternator Good signal, then it'll be autosensing.
Click to expand...
George, the install instructions found here: http://ironpigoffroad.com/tech/iporfj80dualbattinstructions.pdf don't mention anything about wiring it to the alternator. So yea I think it's just wired to the batteries.

As for operation, they list the instructions as follows (also in the install instructions URL mentioned above):

"1. Separator automatically connects batteries when charging current is present and disconnects when voltage drops below 12.8 volts.
2. To engage separator manually simply press and hold momentary switch. (batteries are connected only while switch is pressed, until vehicle starts and charging current is present)"

What's the actual part number and make of the isolator?
Click to expand...
Here ya go.

Thanks!
Isolater.webp
 
Well, it's autosensing and it will engage with the charger since the main battery voltage will show >13.2V.

So, it will confuse the charger since the solenoid likely draws at least half an amp and so it'll take a long time to decide the battery is actually topped up.

cheers,
george.
 
Yes, it'll charge both since the autosensing combiner will engage the solenoid.

Ok or Not?? Well, it really all depends on the tender and how it interacts with the current being drawn to energize the solenoid when above 13.2V (per the spec of the surepower you are using).

For long term battery charging with a smart tender, the whole point is that it will take the battery up to the 14.4V point to fully charge it and then it will revert to a float charge level around 13.5V or thereabouts. You do NOT want to keep driving 14.4V into a battery during long term float.

So, you need to get a multimeter and see what the tender you are using does when it claims to have fully charged the battery. See what voltage is being applied long term. Around 13.5V is good, around 14.4V is bad...

cheers,
george.
 
george_tlc said:
Yes, it'll charge both since the autosensing combiner will engage the solenoid.

Ok or Not?? Well, it really all depends on the tender and how it interacts with the current being drawn to energize the solenoid when above 13.2V (per the spec of the surepower you are using).

For long term battery charging with a smart tender, the whole point is that it will take the battery up to the 14.4V point to fully charge it and then it will revert to a float charge level around 13.5V or thereabouts. You do NOT want to keep driving 14.4V into a battery during long term float.

So, you need to get a multimeter and see what the tender you are using does when it claims to have fully charged the battery. See what voltage is being applied long term. Around 13.5V is good, around 14.4V is bad...

cheers,
george.
Click to expand...
Ok so here's my dumb question for ya lol. Where do I hook up the voltmeter? To the charger's positive terminal (while connected to the primary battery)?
 
Set the multimeter on VOLTS range and probe across the +/- of the main battery. Since both batteries should be combined with the tender connected (you can confirm by measuring across the aux bat) they should essentially read the same voltage - which will be what the tender is outputting.

cheers,
george.
 
I would put a battery shut off on the Aux batt and charge them separate. You wouldn't looses your presets that way.
Disconnect the Aux batt and charge your starter batt first. Than charge your Aux or buy another charger and charge the Aux batt at the same time.
 
George,

Takes a lot longer (> 24 hrs) to charge with the trickle charger connected to the primary battery, but the #s on the voltmeter look great:

- 14.4V when actively charging
- 13.5V when fully charged & floating

Thanks!
 
Ok so I have another question. My radiator recently failed, and I took it into a local shop to get replaced. I think they may have somehow messed up the connection for the dual battery kit. I say this because typically when I place my batter charger/maintainer on the primary battery, after a few seconds, I hear a loud CLICK, which I believe is the solenoid connecting the circuit between both batteries. And then both batteries get (re)charged simultaneously.

I don't hear this click anymore when I'm charging the battery, and the primary battery got fully charged. Then I connected the charger to the secondary battery, and it was NOT fully charged...and required several hours to reach fully charged status.

So my question is, is there a way I can tell for sure if the dual battery "setup" is still functional, or if I need to take it back to the shop to fix whatever they did?
 
Where do you have the earth for second battery?
 
It was a longshot, but i thought maybe when they removed the radiator they may have disconnected the earth cable (where it connects to body/frame) of your second battery.

The cable im talking about is the large black electrical lead that comes off your earth terminal and is then bolted either to your frame or engine block, though i have seen some earthed to the body. If this cable does not have a good connection then it will not charge.

Also i would be checking the connections of the battery controller for same issues (earthing points, corrosion, lugs not soldered/crimped on properly, loose bolts/screws on lugs, etc).

Good hunting :)
 
You must log in or register to reply here.

Share this page

Back
Top Bottom