Dual batteries, DC to DC chargers, isolators, AGM... HELP!

[unsavory]

Apologies for the long post, but I've been super impressed with the technical knowledge I've seen in on this forum and am hoping someone might be able to help.

I own a 2019 Jeep Wrangler, and have installed a Genesis dual battery system into it for running various accessories. The system is basically two 12v Odyssey dual purpose AGM batteries, with a smart isolator between them, that will automatically disconnect the accessory battery from the starting battery when a certain voltage is reached to avoid draining the starter battery, and then reconnect them when the vehicle is running for charging.

The problem I am having, is that I am not able to get these Odyssey batteries to charge properly in the Jeep Wrangler, because it has a very funky "smart charging system", that varies the charging voltage as you are driving to "save gas mileage". The voltage will fluctuate between 12.7v and 14.7v depending on the battery voltage and accelerator pedal.

Apparently Odyssey batteries only like to be charged at 14.7 volts for bulk charging, and 13.7 for float charging to top them off.

So now I'm looking into DC to DC chargers in order to get my charging voltages up to the correct level. Has anyone had any luck installing a DC to DC charger along side an already existing dual battery system that has a smart isolator built into it?

All of the DC to DC chargers seem to want the starter battery separated from the accessory battery, as they already have an isolator built in.

The other option I am exploring, is just disabling the smart charging in the Jeep by disconnecting the Intelligent Battery Sensor. But this causes the alternator to put out a constant 14.5v, and I'm worried this will actually OVERCHARGE my batteries... but I'm not sure?

Any other creative ideas I can try?

[theoldwizard1]

RLS7201 wrote:
If like my CRV, you charging system will stay at 14.7 when you turn on the headlights. No trickery necessary.

Don't bet on "smart charging" working that way on all vehicles, or even on other Hondas.

[theoldwizard1]

unsavory wrote:
Any idea what the potential repercussions might be? Everything seems to be working correctly with the battery sensor disconnected, other than the voltage just sits there at 14.7V instead of fluctuating with engine speed.

At a continuous 14.7V, you will kill your battery in MONTHS !

[RLS7201]

If like my CRV, you charging system will stay at 14.7 when you turn on the headlights. No trickery necessary.

Richard

[NRALIFR]

Since the OEM charging system apparently supports AGM, I wouldn’t put the OEM starting battery back in. But, it’s apparently unable to keep both of your Odyssey AGM’s properly charged.

I still think a DC-DC charger could help you, but I confess I’m having a hard time imagining how to install it so that it plays well with the charge controller that’s part of your Genesis system. The Cole Hersee charge controller with your system connects the two batteries together any time either of them are over 13.2 volts. It would be nice if it had an upper voltage limit that it would disconnect at as well, but it doesn’t. It does limit the amperage between the batteries to 15 amps though. How the DC-DC charger will behave when the two batteries are connected through the Genesis solenoid is what I can’t imagine.

I think it would be better if the two Odyssey’s were separated all the time, except when you need them for emergency starting. That way, a DC-DC charger could be installed between them, and it would be simply another load on the starting battery and it’s charging system. But then you would need to make sure all of your “engine stopped” accessory loads are connected to the second battery.

Renogy, Redarc, and CTEK all make DC-DC chargers you could check out. I have a Redarc 25 amp in my camper, and I know it’s sealed and rated for under hood installation. Renogy and Redarc both make a 40 amp model, not sure about CTEK. I would think a 25 amp charger would be sufficient for a group 25 AGM.

:):)

[unsavory]

theoldwizard1 wrote:

unsavory wrote:
The other option I am exploring, is just disabling the smart charging in the Jeep by disconnecting the Intelligent Battery Sensor. But this causes the alternator to put out a constant 14.5v, and I'm worried this will actually OVERCHARGE my batteries... but I'm not sure?

DON'T DO IT ! The computer module is very smart and trying to trick it, is not a good idea.

Any idea what the potential repercussions might be? Everything seems to be working correctly with the battery sensor disconnected, other than the voltage just sits there at 14.7V instead of fluctuating with engine speed.

NRALIFR wrote:
I had to do some quick reading about this system as I’m not familiar with it. It appears that it replaces the OEM battery with two AGM’s that have a smart isolator between them, correct?

Yes, that is correct, and one of the reasons I would like to keep the Genesis system in tact, is that it has the cool ability to use the secondary battery to jump start the primary starting battery by connecting the two batteries together with the push of a button.

NRALIFR wrote:
What was the OEM starting battery? Flooded, or AGM?

The OEM setup was two AGM batteries. One of them, for the Electronic Stop Start system, was a tiny little AGM hidden below the main battery. It is used to run the accessories at a stop light. The problem is, if that dinky little battery fails, and they do fail prematurely often... the Jeep refuses to start off the starting battery! It's a horribly designed system.

Even though the OEM has AGM batteries, it seems the Odyssey batteries in particular are very finicky about charging profiles. More than any other AGM battery. They require no less than 13.8 V float charge, or they will self discharge even if the input volts are something like 13.2 - 13.4.

NRALIFR wrote:
If the OEM starting battery wasn’t AGM, you might consider reinstalling it as the starting battery, and selling or repurposing the AGM.

That's not a bad option I guess. Except the OEM battery will not fit anymore with the Genesis dual battery tray. There's no room for the OEM battery anymore. I guess I could replace the Odyssey group 25 starting battery with a different AGM that isn't as picky about how it's charged, but I also heard it is bad to mix battery types with the Genesis system.

LittleBill wrote:
i have to say im confused. this looks like a custom designed product for the jeep? an expensive one that's for sure? i find it hard to believe they didn't design for this.

I'm not sure they've had time to fully test this, since the JL Wrangler is only 2 years old, and the product was released I think less than a year after the JL's release. It could be that they didn't run into the issue with the Odyssey charging profile.

[landyacht318]

A deeply discharged Odyssey AGM, ideally, wants 40 amps applied per 100Ah of capacity until 14.7v is reached, then hold 14.7v for 4 more hours then float at 13.6 to 13.8v.



Do you have a plug in charging source capable of this?

Few do, as few exist.

80% charged to 100% charged is not going to happen in less than 3.5 hours even if you achieve 14.7v at battery terminals and drive 3.5+ hours.

Expecting your vehicle's charging system to do an Ideal job , even if you drive for 3.5 hours, is unwise.

The drop to 12.7v for fuel savings only makes it worse, and the system, with two Odyssey batteries, which retain surface charge voltage higher and longer than a regular starting battery, will likely having them not only powering the vehicles electrical loads while underway, but also feeding into engine starting battery when it decides 12.7v is fine and dandy.

Seeing as how you are not even going to come close to being able to achieve ideal recharging via your vehicles charging system, I recommend accepting whatever your vehicle's voltage regulator allows, and then having a plug in charging source that can meet the 40 amps upto 14.7v, hold for 4 hours, per 100Ah of capacity requirement/recommendation.

It would be best to hook up this charger in their most depleted state.

You can of course get away with much less, and it will be philosophically 'just fine' for a period of time, but your 300$+ Odyssey AGMS will fail to live up to their potential.

I have cycled a Northstar AGM group27 to death at 6 years and 1200+ deep cycles and thousands of shallow cycles. Northstar has the same pure lead thin plate construction, and it indeed LOVES the high amp recharge to full.

Its voltage retention and engine cranking gusto is extremely obviously better after it gets a huge charge rate from a well depleted state and this is more and more apparent the more often it gets less than a huge charging rate and charged to less than full cycle after cycle.

I have fooled my 1989 engine computer with a 10ohm 50 watt resistor into thinking it is still attached to the externally regulated alternator, and no check engine light. I use a modified adjustable external voltage regulator whose voltage adjustment knob is on my Dashboard. I have one of the very few vehicles that can indeed fully charge a depleted battery to full in the minimum time safely possible but the 3.5 hours minimum, from 80% to 100% still applies.

Beware of idling to recharge. Underhood airflow and higher alternator fan rpm plays a huge part in alternator cooling, and Depleted Odysey AGMS can easily suck up 50+ amps each and fry your alternator, if it was told to deliver 14.2+v to the batteries.

The DC to Dc converter, unless it has an alternator temp sensor, can overheat the alternator even when the vehicle decides 12.7v is fine and dandy.

Any charging is of course better than no recharging of a depleted battery, but treating a pair of Odyssey AGMS correctly, to get them to live upto their potential, requires those high amp recharge parameters be met every few deep cycles .

[NRALIFR]

I had to do some quick reading about this system as I’m not familiar with it. It appears that it replaces the OEM battery with two AGM’s that have a smart isolator between them, correct?

What was the OEM starting battery? Flooded, or AGM?

A DC-DC charger could be added to keep the second battery charged correctly. It will do nothing for the starting battery though, so hopefully the Jeep’s charging system supports AGM. If not, I would not have purchased this system.

IMO, a DC-DC charger could be installed between the starting battery and the second battery. But, it would need its own isolation solenoid (non-intelligent, not voltage sensing) on the input wire to the charger that is only energized when the engine is running. Otherwise, the DC-DC charger would continue to charge the second battery when the engine is off.

Voltage from the second battery will not back feed to the starting battery through the DC-DC charger. It will boost the voltage going to the second battery though, and provided it supports AGM charging, will keep it fully charged. Let the Jeep charging system keep the starting battery charged, and leave the Genesis system intact so it’s fully functional.

If the OEM starting battery wasn’t AGM, you might consider reinstalling it as the starting battery, and selling or repurposing the AGM.

:):)

[time2roll]

You will not be able to use both the isolator and the DC-DC charger.

Is the start battery floundering?

Depending on your accessories you may want to go back to the oem start battery and DC-DC charge one or two Odyssey to be used for accessories only.

[theoldwizard1]

unsavory wrote:
The problem I am having, is that I am not able to get these Odyssey batteries to charge properly in the Jeep Wrangler, because it has a very funky "smart charging system", that varies the charging voltage as you are driving to "save gas mileage".

Yep ! Pretty standard on almost every vehicle from about 2005.

unsavory wrote:
All of the DC to DC chargers seem to want the starter battery separated from the accessory battery, as they already have an isolator built in.

Follow the instructions ! What you are missing is that theses DC-DC chargers actually boost the voltage going to the second battery so that it get the correct voltage no matter what is being sent to the starting battery.

unsavory wrote:
The other option I am exploring, is just disabling the smart charging in the Jeep by disconnecting the Intelligent Battery Sensor. But this causes the alternator to put out a constant 14.5v, and I'm worried this will actually OVERCHARGE my batteries... but I'm not sure?

DON'T DO IT ! The computer module is very smart and trying to trick it, is not a good idea.

If the charging characteristics of the Odyssey AGM batteries are that different compared to a normal "flooded" lead acid, re-install a plain battery as your starting battery.

[LittleBill]

i have to say im confused. this looks like a custom designed product for the jeep? an expensive one that's for sure? i find it hard to believe they didn't design for this.

that said if your just using the secondary battery and don't need it combined, then its easy, disconnect the second battery, connect the dc-dc charger to output of the second battery wiring from the genesis kit, and connect the output of the dc-dc to the second battery and that should be it.