Has Anyone Put a Battery Tender on their Auxiliary Battery?

[ShadowsPapa]

Conflicting info I am seeing. Some say you can’t tend just the main battery as it won’t charge the aux. which is what I have been seeing since I started using a fender. Mine is wired to the main batteries positive and negative posts.

Tons of bad "crap" "info" out there.
The two batteries ARE absolutely connected together. Any tender WILL charge both.
If yours is wired that way you are charging both. Do not connect to the negative post directly. Only the top studs.

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[rbryant76]

So a bit ago my tender shows full charge. The aux switches do not come on. When started it shows aux battery charging aux switches disabled. I know if I let it run for a bit it will let the switches work. The Jeep is not driven much at all. 7k miles in about 3 years. Have dealt with this for a while just now decided to track it down.

 

[ShadowsPapa]

So a bit ago my tender shows full charge. The aux switches do not come on. When started it shows aux battery charging aux switches disabled. I know if I let it run for a bit it will let the switches work. The Jeep is not driven much at all. 7k miles in about 3 years. Have dealt with this for a while just now decided to track it down.

Bet it's time for new batteries. Lack of driving is really hard on them and 3 years is about par for the course.

 

[rbryant76]

Maybe. But I have kept it on a tender regularly. Again just decided to look into how to keep the aux charged.

 

[ShadowsPapa]

Maybe. But I have kept it on a tender regularly. Again just decided to look into how to keep the aux charged.

Since new?
3 years is pretty typical.
When you connect a charger you ARE charging both.
Never connect a charger or tender below the IBS on the negative terminal.

 

[staying_tuned]

Cascadia’s hood panel trickle charges while offering a 12v out. Covered storage would pose a problem but I had it backed into our car port at the previous home and it still gathered enough light to keep it topped off in winter.

 

[ShadowsPapa]

Maybe. But I have kept it on a tender regularly. Again just decided to look into how to keep the aux charged.

OK, back to a REAL computer, not the tiny phone.
The aux battery isn't typically needing charged any more than the crank/main battery.
They are literally tied together, in parallel when the truck is off in your garage, or running on the road.
This means it's being charged as you drive it - unless you blew the N3 fuse somehow.
Charging by putting clamps on the main battery charges both at the same time.
The only way this would fail is if either is bad and not taking the charge. But since they are in parallel many chargers may not see a "bad battery".

So driving it charges both, and a tender charges both.

Only charge with the negative charger clamp above the IBS, as in the green circle here, never directly at the terminal or IBS clamp unless you remove and reset the IBS.

 

[JETNC]

What does IBS stand for?

 

[sharpsicle]

What does IBS stand for?

Irritable Bowel Syn... oh wait. Wrong forum.

It stands for Intelligent Battery Sensor.

 

[ShadowsPapa]

Irritable Bowel Syn... oh wait. Wrong forum.

It stands for Intelligent Battery Sensor.

I like your first thought better........... it does give some heartburn so maybe you are right?

 

[HankB]

I’ve just come across this thread, so my apologies for jumping in late. My experience with multi battery set ups in boats suggest something’s not right with this setup, or Jeep has a magic black box involved. With boat systems batteries come in banks, both for engines and house functions. And they may be charged from multiple sources, engine alternators, shore power chargers, and generators.

The cardinal rule in all cases is that all batteries of a bank be identical in type, capacity and most importantly charging profile. And when it comes to replacing, banks are replaced in their entirety, not piecemeal. The reason being that the charging systems all charge until they sense a battery in charged state, first battery charged and then all charging stops for the bank. This is kind of a universal thing. It was the same on every boat I’ve come in contact with, as well as gas and diesel power plants and heavy duty inverter chargers.

So with that, how does Jeep get two very different batteries to charge properly when connected in parallel?

 

[ShadowsPapa]

I’ve just come across this thread, so my apologies for jumping in late. My experience with multi battery set ups in boats suggest something’s not right with this setup, or Jeep has a magic black box involved. With boat systems batteries come in banks, both for engines and house functions. And they may be charged from multiple sources, engine alternators, shore power chargers, and generators.

The cardinal rule in all cases is that all batteries of a bank be identical in type, capacity and most importantly charging profile. And when it comes to replacing, banks are replaced in their entirety, not piecemeal. The reason being that the charging systems all charge until they sense a battery in charged state, first battery charged and then all charging stops for the bank. This is kind of a universal thing. It was the same on every boat I’ve come in contact with, as well as gas and diesel power plants and heavy duty inverter chargers.

So with that, how does Jeep get two very different batteries to charge properly when connected in parallel?

Apples and oranges.
Boats and RVs and such with banks of batteries are very different.
Plus - the cardinal rule has been challenged and found to not be absolute.
And if you dig deep enough, you will even find battery sellers and manufacturers state that the "identical size" isn't really necessary. Ideal, but the "common knowledge" came about years ago and no one challenged it - until recently.

When in parallel, it's as if you are charging one big battery.

Age is the bigger matter. Resistance to charge changes, capacity changes, it's harder to charge an old battery with many cycles under its belt.

It's sort of like - there are still people who swear that to test an alternator on your 1980 Camaro, you pull a battery cable off and if it still runs, it's charging.
That's a NO NO NO NO! that should have died with generators, and yet it's lore that to this day, still gets passed forward. Why? Because it's the internet, people talk and "did you know" and no one ever questions it. You will blow stuff if you pull that crap with an alternator, even a 1965 alternator.

Anyway, batteries in parallel are similar to a bigger battery, single unit. The one with the higher voltage will "charge" the one with the lower voltage until they reach an equilibrium. That is likely going to be lower than a full charge for the pair. Proper, correct charging takes time and AGM batteries go through charging phases (at least with a smart charger) so they should end up both being 100% charged - unless one is OLD and has reduced capacity, and increased resistance.
If both batteries are 1-2 years old, replacing one can work out ok. If older, it's wiser to replace both. But size doesn't matter and some RV sites say even age it's a big deal.

Now in SERIES, it's a huge no-no. Don't mix battery ages and sizes in series. You'll kill the smaller battery.

In short - the batteries in parallel thing seems to be an old myth or something passed down for generations and it just won't die.

Maybe they are talking about SERIES batteries like some tractors and other equipment have used. There it's a big deal.
But parallel, the more I learn, and dig through my old books, the more I see - as long as they are the same voltage, same technology (never mix AGM and lithium, for example - so if you think you are being clever and swapping out ONE battery for lithium, you are being foolish, not smart)

 

[HankB]

Apples and oranges.
Boats and RVs and such with banks of batteries are very different.
Plus - the cardinal rule has been challenged and found to not be absolute.
And if you dig deep enough, you will even find battery sellers and manufacturers state that the "identical size" isn't really necessary. Ideal, but the "common knowledge" came about years ago and no one challenged it - until recently.

When in parallel, it's as if you are charging one big battery.

Age is the bigger matter. Resistance to charge changes, capacity changes, it's harder to charge an old battery with many cycles under its belt.

It's sort of like - there are still people who swear that to test an alternator on your 1980 Camaro, you pull a battery cable off and if it still runs, it's charging.
That's a NO NO NO NO! that should have died with generators, and yet it's lore that to this day, still gets passed forward. Why? Because it's the internet, people talk and "did you know" and no one ever questions it. You will blow stuff if you pull that crap with an alternator, even a 1965 alternator.

Anyway, batteries in parallel are similar to a bigger battery, single unit. The one with the higher voltage will "charge" the one with the lower voltage until they reach an equilibrium. That is likely going to be lower than a full charge for the pair. Proper, correct charging takes time and AGM batteries go through charging phases (at least with a smart charger) so they should end up both being 100% charged - unless one is OLD and has reduced capacity, and increased resistance.
If both batteries are 1-2 years old, replacing one can work out ok. If older, it's wiser to replace both. But size doesn't matter and some RV sites say even age it's a big deal.

Now in SERIES, it's a huge no-no. Don't mix battery ages and sizes in series. You'll kill the smaller battery.

In short - the batteries in parallel thing seems to be an old myth or something passed down for generations and it just won't die.

Maybe they are talking about SERIES batteries like some tractors and other equipment have used. There it's a big deal.
But parallel, the more I learn, and dig through my old books, the more I see - as long as they are the same voltage, same technology (never mix AGM and lithium, for example - so if you think you are being clever and swapping out ONE battery for lithium, you are being foolish, not smart)

Thanks. Yes, i’m familiar with the practice of using two 6 volt batteries in series to create a higher amp 12 volt starting source for big diesels. But I think both of us are dating ourselves with that recollection. I think better battery technology and manufacturing, as well as lower related maintenance, and fuel efficiency weight control, has pretty much done away with that set up. In any event, boats work off of parallel setups to maximize available amps.

I think the “identical “ aspect is more of safety net for the typical boat owner who may, or may not, be capable of determining if a replacement battery is close enough to be paired with an existing one in a bank.

I get your argument that once the first battery reaches a full charge state (and charging shuts down) it will provide the power to allow the undercharged twin to reach equilibrium. I’m fine with that when they are both the same capacity battery.

But the jeep Aux battery is a larger version of coin batteries that are placed in electronic devices to keep system settings in memory alive while main power is off. As such it is physically much smaller than the starting battery. Wouldn’t that cause it to be charged first? That being the case, the smaller Aux battery would seem incapable of charging up the undercharged starting battery. So wouldn’t that mean a maintainer would end up constantly charging the Aux because the Aux was running a rapid cycle of charge discharges as it attempts to bring the starting battery up to charge?

Just to be clear, I am not trying to pick a fight. I’m also confident the engineers at jeep know what they’re doing (most of the time). But My old mechanical engineer brain is still stuck on the circuit theory it was fed in the 60s and 70s (and I’m still of the belief that it is all electrickery.) So what am I missing?

 

[ShadowsPapa]

But the jeep Aux battery is a larger version of coin batteries that are placed in electronic devices to keep system settings in memory alive while main power is off. As such it is physically much smaller than the starting battery. Wouldn’t that cause it to be charged first? That being the case, the smaller Aux battery would seem incapable of charging up the undercharged starting battery. So wouldn’t that mean a maintainer would end up constantly charging the Aux because the Aux was running a rapid cycle of charge discharges as it attempts to bring the starting battery up to charge?

Since the batteries are in parallel at all times EXCEPT during an ESS event, and the main battery supplies the EHPS pump and fan while the aux battery supplies the internal electronics, radio and such while they are disconnected during an ESS event, they actually both discharge. I've had volt meters connected so that you could watch the voltages during an ESS stop - the only time they aren't connected, and found both actually discharge fairly similarly during that time.
When your truck is sitting in your garage for days - both batteries discharge together, each to its own ability to supply power. Both actually supply the electronics as the main is also connected to the N1 terminal for the electronics via the PCR which remains closed. So if you have a drain in the truck, say you've powered the USB or 12v outlet to not shut off with the truck, you'd end up killing both batteries. If you connect a charger, you charge both batteries. It works fine. Done it multiple times. Both will reach full charge if they aren't damaged.

When you start the Jeep, both batteries are still connected to each other, while you drive, and when parked, they are constantly in parallel.
There's never a time that the aux battery would be trying to charge the larger battery. When would that ever happen? Unless you had a bad main battery............. then you'd go out to find your truck won't start if the voltage drops too low.

I've found a couple of decent explanations with the solar guys that of course run banks of batteries and talk about this a lot (been digging because we've talked of solar at home) ->


It works because the batteries discharge at the same voltage decay rate if you will. The voltage must stay the same since they are in parallel.

A 10 Ah battery will deliver only 1/10 th of what a 100 Ah battery will to decay in voltage the same amount. Therefore it delivers what it can as it discharges. The 100 Ah battery delivers approximately 10 times as much to drop it’s voltage the same amount.


An engineer wrote this:
Take two LiFePO4 batteries, even at different states of charge but at the same voltage. What happens if you initially parallel them? Answer: nothing. They'll just sit there, both with their own BMS. Now you provide a charge source. Both batteries will start charging but one will take more charge current than the other even at the same state of charge (and voltage). The reason being that the internal resistance of one will be different than the other, based on the state of charge
In the end they'll reach the same state of charge. And they will happily split the load between them, and share the charge current between them. The only things you need to do is:
- Make sure you cables are approximately the same length and the overall resistance from their connection to the bus bars to the battery packs is the same
- Make sure that each BMS can handle the full load in case one battery pack disconnects.
- Only do this with batteries of the same chemistry

 

[chorky]

OK, back to a REAL computer, not the tiny phone.
The aux battery isn't typically needing charged any more than the crank/main battery.
They are literally tied together, in parallel when the truck is off in your garage, or running on the road.
This means it's being charged as you drive it - unless you blew the N3 fuse somehow.
Charging by putting clamps on the main battery charges both at the same time.
The only way this would fail is if either is bad and not taking the charge. But since they are in parallel many chargers may not see a "bad battery".

So driving it charges both, and a tender charges both.

Only charge with the negative charger clamp above the IBS, as in the green circle here, never directly at the terminal or IBS clamp unless you remove and reset the IBS.

Ok so heres a thought. The purpose of the IBS i for the PcM to basically track what is doing in and out of the battery. But the IBS is on top of the primary battery. So I see easily how it can track power going in and out of that battery but how on earth does it even understand what the status of the aux bttery is?

i noticed that for example the Genesis system is wired essentially the same. But in either case the voltage of only one battery is being accurately tracked. im surprised this hasnt been discussed…unless I missed that convo

Apples and oranges.
Boats and RVs and such with banks of batteries are very different.
Plus - the cardinal rule has been challenged and found to not be absolute.
And if you dig deep enough, you will even find battery sellers and manufacturers state that the "identical size" isn't really necessary. Ideal, but the "common knowledge" came about years ago and no one challenged it - until recently.

When in parallel, it's as if you are charging one big battery.

Age is the bigger matter. Resistance to charge changes, capacity changes, it's harder to charge an old battery with many cycles under its belt.

It's sort of like - there are still people who swear that to test an alternator on your 1980 Camaro, you pull a battery cable off and if it still runs, it's charging.
That's a NO NO NO NO! that should have died with generators, and yet it's lore that to this day, still gets passed forward. Why? Because it's the internet, people talk and "did you know" and no one ever questions it. You will blow stuff if you pull that crap with an alternator, even a 1965 alternator.

Anyway, batteries in parallel are similar to a bigger battery, single unit. The one with the higher voltage will "charge" the one with the lower voltage until they reach an equilibrium. That is likely going to be lower than a full charge for the pair. Proper, correct charging takes time and AGM batteries go through charging phases (at least with a smart charger) so they should end up both being 100% charged - unless one is OLD and has reduced capacity, and increased resistance.
If both batteries are 1-2 years old, replacing one can work out ok. If older, it's wiser to replace both. But size doesn't matter and some RV sites say even age it's a big deal.

Now in SERIES, it's a huge no-no. Don't mix battery ages and sizes in series. You'll kill the smaller battery.

In short - the batteries in parallel thing seems to be an old myth or something passed down for generations and it just won't die.

Maybe they are talking about SERIES batteries like some tractors and other equipment have used. There it's a big deal.
But parallel, the more I learn, and dig through my old books, the more I see - as long as they are the same voltage, same technology (never mix AGM and lithium, for example - so if you think you are being clever and swapping out ONE battery for lithium, you are being foolish, not smart)

so with this isnt there still damage being done? Even with parallel charging I always thought that unequal charge percentages of like batteries still reduced life expectancy.

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