Dual battery problem

tpreston

New member
I have a 2010 Jeep JK Unlimited. I installed a dual battery system about 4 years ago. Electrically it contained a Cole Hersee smart battery isolator. I installed 2 Optima Yellow top batteries. After about 2 years the main battery failed and I replaced it. Otherwise no issues.
I have been traveling for work and haven't driven the Jeep in 2 weeks. I try to start it and nothing but a click. Main battery was dead. Second battery was fine so I switched the positions. I tried to charge the main battery and it would not take charge. I had the main battery tested at a parts store and they said per their machine it had a bad cell and would not charge.
So I am beginning to think that something isn't right. I've decided not to go back to another Optima battery. I've also decided to replace the isolator, mainly because I don't know how to test it. A new one is not that expensive. I'm going to try a Stinger SGP32.
My main question is can I go with a regular lead/acid battery and the Optima AGM type battery with my dual battery setup or should I make both batteries the same?
Feel free to comment/criticize my thought on replacing the isolator as well

Thanks
 

v_man

Explorer
My main question is can I go with a regular lead/acid battery and the Optima AGM type battery with my dual battery setup or should I make both batteries the same?

I spent a fair amount of time researching this question before my dual setup in my LX. My take away was that age of the two batteries and their state of charge was more important than matching battery brands or types. So I went with (2) new batteries, a flooded Bosch starting battery and an Optima yellow top for the house battery.

When one battery is new and the other is old, the older battery with lower volts will always draw from the newer battery with higher volts. (When they are connected via the solenoid) The two batteries always want to equalize their state of charge. No issues so far with my setup as described ...
 
A simple isolator or voltage sensing relay shouldn't be harming the starting battery at all. As others have said; your auxilliary battery is more likely to be 'harmed', particularly if its a deep cycle because its frequently only being charged over and over to about 80% by your cars alternator,which is intended to charge a starting battery. As long as your vsr is working right and ensuring the starter is getting up to voltage before allowing flow to the auxiliary I cant see how it would harm the starter.
 

john61ct

Adventurer
Optima is fine for cranking, but if your House battery is used for deep cycling then get a proper bank designed for that. What loads?

If your only charge source is alt while driving then ignition solenoid is fine for that.

How are you ensuring keeping House over 50% SoC?
 

tpreston

New member
The primary battery was just for regular functions with no big loads. I have my winch (rarely used), and my auxiliary lights run through an Spod, all go through the secondary battery.
My alternator is the stock unit and while it is 7 years old my volt meter in my Aero Force gauge has been showing 14.2 volts consistently when driving.
The interesting thing is the secondary battery has had no issues. I know it has not been used as much as the primary, but it has keep its charge which means the isolator was making sure it was getting charge. But it has outlasted 2 primary batteries!
Maybe, as mentioned above, with the different ages the older battery has been drawing down the newer primary battery.
Since the secondary is over 4 years old I will replace it as well and keep both batteries the same type and age.
It also sounds like I shouldn't need to replace the isolator.
 

DaveInDenver

Middle Income Semi-Redneck
Most of the time having differing batteries isn't a problem in dual battery systems. It's critical that batteries be matched closely when they are parallel all the time, meaning under load and charging. If they only get paralleled while charging you have more wiggle room to mix and match.

My alternator is the stock unit and while it is 7 years old my volt meter in my Aero Force gauge has been showing 14.2 volts consistently when driving.
If that is really the case then that's your problem. You may be seriously undercharging your batteries. AGM in particular needs to be higher, ideally 14.6V up to 14.8V or even higher. Each time you discharge and do not fully recharge consumes a little bit of life. Vehicle charging systems aren't ideal and even working well (which will typically see 14.4V or so at the battery) need to augmented with a good external charger periodically to maximize life of batteries. I put my Odysseys on a wall charger about once a month to get them really topped.

You should measure right at the battery with a good meter to check this since there will be a lot of variables involved with measurement and car wiring. Ultimately it's what the battery is seeing that's important.

The interesting thing is the secondary battery has had no issues. I know it has not been used as much as the primary, but it has keep its charge which means the isolator was making sure it was getting charge. But it has outlasted 2 primary batteries!
Maybe, as mentioned above, with the different ages the older battery has been drawing down the newer primary battery.
Since the secondary is over 4 years old I will replace it as well and keep both batteries the same type and age.
It also sounds like I shouldn't need to replace the isolator.
I doubt the isolator is a problem.
 

Ducky's Dad

Explorer
Since the starting battery is failing, check parasitic drain. There may be something drawing down that battery while the Jeep is parked. Drain plus sulfation plus not reconditioning on AGM charger can kill a battery over a year or two.
 

dwh

Tail-End Charlie
Um...no, no and, well...no.

Lead-acid batteries come in sealed or vented (removable caps, can add water). Vented are always flooded (sloshy electrolyte).

Sealed lead-acid batteries can be flooded lead-acid (FLA), or they can have fiberglass fabric between the plates to act as a sponge for the electrolyte. That's called absorbed glass mat (AGM). Or sealed can also come with a gelling agent added to the electrolyte to make the electrolyte a sort of paste. That's called gelled electrolyte (GEL).

FLA, AGM and GEL are ALL "lead-acid" batteries.

In regards to charging, they are basically the same, except that FLA and AGM will charge faster and stay healthy longer if pushed to higher voltages, like 14.4v-14.8v...as long as they don't get too hot when doing it. GEL would also charge faster and live longer if pushed to higher voltages, except that higher voltages and temperatures tends to break down the gelling agent, so most GELs recommend not going over 14.2v.


Optimas are AGMs, with a twist. Literally. (Optima, feel free to send me a check for that new marketing slogan. :) ) They take the positive plates, negative plates and fiberglass fabric and roll it up. That's called spiral-wound AGM. That's why Optimas look like a six-pack...they ARE a six-pack...of 2v cylindrical cells.

That spiral-wound design has one major side-effect - lower resistance. So a fully drained Optima can be pulled down to a lower voltage than a fully drained flat-plate design. This often fools "smart chargers", which see a lower than expected voltage and then refuse to begin charging. The trick recommended by Optima is to hook up (parallel) a second battery, just long enough for the smart charger to see a higher voltage and start charging, then unhook the second battery.

A lot of Optimas have been returned as "bad battery, won't charge" because of this, when the battery wasn't actually bad. An old dumb charger would have charged it just fine. I can't say for sure, but I would guess that if it can fool a smart charger, it might fool a smart tester as well...

----------------------------

Power does NOT flow from the engine battery to the house battery, except with a dumb solenoid, when the key is turned on, but the engine isn't running. With an ACR (computer controlled solenoid), the solenoid is not engaged until the voltage rises, indicating the alternator is operating.

When the engine is running and the alternator is operating, the alternator has a higher voltage potential, and a lower resistance than either battery. Power flows from alternator to battery A, from alternator to battery B, but not from battery A to battery B.

-----------------------------

Batteries tied into a permanent full-time bank have to be identical. Batteries tied only during charging DO NOT. Different size, age, etc. is completely irrelevant. They don't affect each other.

What matters is that they both require approximately the same charge voltage, and that the charging source supplies approximately that charge voltage. Mixing AGM and FLA is fine - in terms of charging they are the same.

Mixing GEL with AGM or FLA is fine as long as the charging source doesn't exceed 14.2v. Of course, that's not going to be optimal for the AGM or FLA, both of which would prefer a higher voltage, but it will get the job done. Charging GEL from a charge source with a voltage high enough to keep AGM and FLA healthy and happy, won't be healthy for the GEL - over the long term. Ocassionally exceeding the GEL's recommended voltage probably won't hurt it.

----------------------------------


To the OP,

Something is draining your starting battery when the truck is off. What is it?

It may be pulling the Optima down far enough to fool a smart charger (and maybe even a smart tester) into thinking it's a bad battery.


More likely, is that the battery has actually gone bad due to a common problem called, "chronic undercharging". Basically, a parasitic load keeps pulling the battery down, and you don't drive enough to bring the battery back to 100%. It can take a lot of hours (anywhere from 8 to 36) for a voltage-regulated alternator to bring a lead-acid battery back to 100%.

Every second of every day, a process happens inside a lead-acid battery. The process is called "sulphation". It's very similar to a process known as "rust". With rust, an oxygen molecule binds to an iron molecule to become an iron oxide molecule. The metal loses a molecule - a.k.a., corrosion. With sulphation, a sulphur molecule binds to a lead molecule to become a lead sulphate molecule. Again, the metal loses a molecule - corrodes.

When a lead-acid battery is fully charged, sulphation slows pretty much to a standstill. Below 100%, it speeds up. The futher below 100%, the faster it goes. The more time the battery spends below 100%, the sooner the plates corrode and the sooner the battery fails.

Chronic undercharging eats lead-acid batteries. Literally - eats the lead plates.

If your starting batteries are failing due to chronic undercharging, it won't matter what lead-acid battery you replace it with - FLA, AGM, or GEL - it will sulphate and prematurely fail.


If you've got a parasitic load drawing down the starting battery, you've either got to stop that, or start regularly (weekly at least, daily is better) topping off the battery, either with a shore powered charger or solar.
 
Last edited:

dwh

Tail-End Charlie
And here's me, thinking I got up early enough. And here's you guys, still beating me to the punch. :)

Probably shouldn't have taken time for for that second cup of coffee while editing my post...
 

tpreston

New member
Ok, even better. I can save money by continue using the Optima and only get a replacement battery.
Right now I have only the factory wiring running to the main battery. All of the dual battery wiring is disconnected and my Spod and my winch. I have to travel this week for work so next weekend we will see if it starts.
I will need to start tracking down the parasitic drain, which should be fun. But I need to install a transmission cooler first. I just need more time to spend on the Jeep!

Thanks for all of the good information.
 

Ducky's Dad

Explorer
The trick recommended by Optima is to hook up (parallel) a second battery, just long enough for the smart charger to see a higher voltage and start charging, then unhook the second battery.
I have worked around that issue by doing a partial charge of dead AGMs with an old dumb charger to get the voltage up enough for the smart charger to recognize the AGM. Then just switch to the smart charger to finish the charge/recondition cycle. Let the AGM rest overnight, then run the charge/recondition cycle again. Has worked on Optima and Odyssey.
 

dwh

Tail-End Charlie
Good information...can you explain this more? With my vehicle running, and dumb solenoid engaged, I show 14.0 volts on battery A and B. I assumed power was traveling from battery A to battery B. So my assumption is that 14 volts travels from:

alternator > battery A > dumb solenoid > battery B

Actually...

alternator > the terminals of battery A > dumb solenoid > the terminals of battery B


Measuring voltage is tricksy. If you put the probes of your meter across the terminals of the battery, are you reading the battery voltage?

OR, are you reading the source voltage before it goes in to the battery?

Which it is depends on voltage potential. If the source has a higher potential than the battery (it does), then you're reading the source voltage.

Of course, since the battery is regulating the voltage of the charging circuit (until the voltages rises to the point where the voltage regulator takes over), you can infer that the battery voltage is the same as what your meter is showing you. But that's an assumption, not an actual measurement. To actually measure the battery voltage, you have to remove the charging source.


Every time you use a meter to measure voltage, you are creating a short circuit (bypass) and reading the voltage on that bypass. That won't tell you what is happening over on another circuit without the bypass.

This is how people fool themselves into thinking that they are seeing a voltage drop, when actually they aren't.

Real world example: Right now (9:15am) I'm sitting in my camper. I see the bulk charge LED on my solar controller lit up. I also have a plug-in cig lighter voltmeter plugged into a power socket wired to the fuse block wired to the battery.

The voltmeter at the battery shows 12.5v (yea, I ran it down a bit last night with an inverter). Busting out the multimeter and sticking the probes on the charge controller terminals shows...<now, where's that meter...>

36v on the PV terminals
12.9v on the battery terminals

So does that mean there is a .4v drop through the ~16' (one-way distance) of #10 wire between the charge controller and the battery?

No. It means that the Victron MPPT charge controller has decided to regulate its maximum voltage potential to 12.9v. Low enough to get the most amps from the downward voltage conversion, but still high enough for the difference in potential to overcome the battery's resistance and push power to the battery.

As the battery voltage rises, the Victron will keep increasing its regulated potential to stay above battery voltage. Until it hits 14.7v (minus temp compensation), at which point it won't go any higher and once the battery catches up (voltage reaches 14.7v), it will switch from bulk stage to absorb stage.

Right now (9:33am)

12.7 at battery
34v Vmp input to controller
13.3v at controller battery terminals

By putting the probes across the battery terminals of the charge controller, I'm creating a short circuit that bypasses the battery and charge circuit wiring. My meter has a much lower resistance, allowing the full voltage potential of the source to flow through it.

It may appear that I'm reading a drop in voltage from 13.3v at the source "end" to 12.7v at the battery "end" (which is a dumb idea to begin with...a circle has no ends), but that's not actually what my meter is showing me - it's showing the source potential, which doesn't tell me a bloody thing about what the actual operating voltage is over on the charging circuit that I just bypassed. (Well, actually, it does tell me one thing. It tells me that there is no way that charging circuit can be higher than 13.3v.)


Can you clarify but not from battery A to battery B thanks...

The source (alternator, shore charger, solar) has a higher voltage potential (pressure) than either battery. It's injecting power into the system. The batteries are extracting power from the system.

For battery B to suck power from battery A, battery A would have to have a higher voltage potential than the source (it doesn't) - OR - a higher voltage potential than battery B (probably does), AND a lower resistance than the source (it doesn't).

So power flows from the source to each battery - seperately and independently. Each absorbs (extracts from the system) however much it can, depending on its own voltage/resistance vs. the voltage of the system it's connected to.
 

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