Using Aux battery setup for useful purposes

[GATORB8]

Hi James:

As I probably don't need to tell you, the LiFePO4 battery chemistry in Antigravity products (at least their batteries that is), has, as its
Achilles' heel IMHO the inability to charge at below freezing temperatures, without causing damage, unless that charge rate is significantly reduced below that which can safely occur at warmer temperatures.

I assume the battery has a BMS that prevents charging at such low temperatures, much that I'm confident that within a few minutes of vehicle operation the engine bay reaches temperatures, even in Minnesota winters, that allow for the alternator to charge up that battery, but I imagine that trickle charging, with the engine off, might need to involve battery warming blankets in some colder locales.

Thoughts?

I'd have to check the Antigravities, but I'd assume it, like some other available options, are not only temperature protected, but also heated.

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[AndySpill]

If I'm reading you right, whether N1 and N2 are jumped or open, the NC PCR relay would have the two connected unless it was triggered.

That is correct. The PCR is a normally closed relay. As you probably know, this means that in the absence of it being provided electrical current..."triggered" to use your words, the batteries are connected in parallel.

It is my understanding that the only two times in which the PCR is energized are at an instant prior to cold crank, where after it is deenergized prior to the cold crank, and during ESS events.

My understanding is that the Aux battery is intended to work as a "buffer" to maintain sufficient voltage to vehicle modules during starting, kind of like the intent behind a capacitor in audio systems.

This may be true. In fact perhaps even more so at the termination of an ESS event. What I can say is that in my personal testing, having disconnected the ESS Aux battery while the engine is off, the dual AGM JL (early model 2018s without TSB 18-092-19 notwithstanding) will cold crank on the second try and thereafter, provided the main battery has ample starting power, and after successfully cranking, turn ESS off in the dash until the next cold crank in which ample power is found on the ESS battery cables.

Of course "finding ample power on the ESS battery cables" may just as much be a product of reconnecting a well functioning ESS battery as it could be 1) disconnecting that battery permanently, along with 2) pulling Fuse 42, so that pre-crank testing that the dual AGM battery JL does is on what it *thinks* is the ESS battery, having rerouted calls for power from the Aux battery to the main battery, the vehicle none the wiser, through these two steps.

Should the PCR relay be triggered and N1-N2 open, you would open yourself up to over discharging the Aux battery and could result in the Aux battery not providing sufficient voltage on startup (or discharging the main battery to a point it could prevent startup if it's reconnected and the batteries balance).

Agreed. I think this is both the OP's and Genesis Offroad's Gen 3 kits thinking of not reconnecting the batteries until, respectively, for the OP, the crank has successfully occurred, and for Shane at Genesis Offroad, , not reconnecting the batteries after successful engine cranking until the main battery reaches 13.1 volts for 90 seconds.

 

[Heimkehr]

As I probably don't need to tell you, the LiFePO4 battery chemistry in Antigravity products (at least their batteries that is), has, as its Achilles' heel IMHO the inability to charge at below freezing temperatures, without causing damage, unless that charge rate is significantly reduced below that which can safely occur at warmer temperatures.

I assume the battery has a BMS that prevents charging at such low temperatures, much that I'm confident that within a few minutes of vehicle operation the engine bay reaches temperatures, even in Minnesota winters, that allow for the alternator to charge up that battery,...

Thoughts?

I think you need to read more closely my post that you quoted, Andy.

I explicitly mention the use of an Interstate H7 AGM in my Jeep as the now-sole cranking battery. My link to the Antigravity site navigates directly to the lithium jump starter page. That is the limit of my use case for their products, and by extension my recommendation for the brand (meaning, cold under-hood temperatures aren't relevant for me.)

Yes, when installed in vehicles, LiFePO4 batteries may or will require special handling when the mercury drops. Knowing this informed my decision to stick with lead acid -- specifically, AGM -- battery chemistry in my Jeep and both of my motorcycles.



Best,
James

 

[AndySpill]

I think you need to read more closely my post that you quoted, Andy.

I explicitly mention the use of an Interstate H7 AGM in my Jeep as the now-sole cranking battery. My link to the Antigravity site navigates directly to the lithium jump starter page. That is the limit of my use case for their products, and by extension my recommendation for the brand (meaning, cold under-hood temperatures aren't relevant for me.)

Yes, when installed in vehicles, LiFePO4 batteries may or will require special handling when the mercury drops. Knowing this informed my decision to stick with lead acid -- specifically, AGM -- battery chemistry in my Jeep and both of my motorcycles.



Best,
James

I completely got that your link was to their portable jump starter product line having clicked it prior to responding. For the record James never endorsed the battery lineup; I just did a tangent to it.

 

[KimFN24]

The biggest problem with the aux battery and keeping it tied to the charging system/using it in any way is its size. Too small to be meaningful and charging 2 different batteries of different sizes and different states of charge is hard on the whole system. It's the reason why both batteries usually die around the same time. If you want a dual battery set up, spend the $ for a proper one with 2 same size batteries. Or you could just not bring tvs, coffee makers, blenders, and scene lighting and actually camp?

Is there room in a newish Gladiator for two (with a Gen3 relocation kit), Interstate 4 year Super Premium MTZ-94R/H7 batteries?

 

[THAW]

I don't understand this post and could use clarification.

To the extent that I do understand what the OP proposed, when "stationary," which to my mind means parked with the engine off, is sort of recreating the functionality of the Power Control Relay (PCR) during ESS events during such parked situations: the PCR being a normally closed relay that is energized during such ESS events to separate the two batteries, so that the OP can break the connection between the two batteries, so as to not tax the cranking battery while running accessories at, say, a parked camping site.

The small size of the Aux battery limiting this functionality notwithstanding, but in no way detracting from his good concept: one that a bigger Aux battery might address--I am confused as to what appliance draw occurs while parked, that normally occurs exclusively against the Aux battery, as it is my understand that with the PCR deenergized while parked, the batteries are normally connected for either/both to run the small appliance draw during these times.

I've heard of Jerry @Jebiruph describe appliance draw, even during ESS events that does happen against the main battery--I think power steering being one (and likely why ESS events won't engage if the steering wheel is turned too much) but I haven't head of--if I understand you correctly--appliance draw while parked that is the exclusive realm of the Aux battery to provide electrical current for.

That post was about what might happen if the OP implemented his idea to manually separate the batteries at the PCR and use the AUX (ESS) battery to power accessories while stationary.

 

[cbrenthus]

Didn't read the whole thread, but I have run both a JLUR and a Chrysler Pacifica with a single battery and the PCR removed for years. Simple answer - unplug the PCR and put a battery selector switch (easy to find for boats) on the negatives of both batteries. Engine off, want to run the radio? Pop the hood and select AUX. When you're ready to start, put it back to the main, or both, and start and drive around for awhile until everything is charged, then set it back to main.

 

[AndySpill]

That post was about what might happen if the OP implemented his idea to manually separate the batteries at the PCR and use the AUX (ESS) battery to power accessories while stationary.

I know what the post was about.

What I don't know is what factory appliances might be run off the Aux battery in the dual AGM JL while at rest, particularly if the OP disconnects the Aux battery, as proposed, from all but the accessories he seeks to run off it during the duration of his camping--or at least disconnects it from the main battery? I think Matt @GATORB8 addressed this.

To rephrase, you wrote that "the AUX (ESS) battery might have to power post ignition-off Jeep electronics processes (e g. evap system) without the help of the CR[an]K (aka main) battery" and I sought to know more about what those processes were.

Regardless, I'd imagine with a temporary fused jumper between N1 and N2 during such an outing that those electrical needs could be rerouted to the cranking battery.

I get that the Aux battery is hardly suited for heavy camping appliance draw. I just wanted to know, this practical fact notwithstanding and addressed by a larger battery, what factory things the Aux battery powers alone when the dual AGM battery JL is parked (i.e. "post ignition" as you say) and that Aux battery is potentially isolated from the main battery.

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