Dual Battery setup with different batteries

[1911]

What Dual Battery system do you run?

On my FJC, I bought this one from Dirty Parts: http://www.dirtyparts.com/store/detail.cfm/FJ-CRUISER-DUAL-BATTERY-KIT/pid-83094

On my 40, I'm putting together my own system based on what I learned from the Dirty Parts kit (it will be similar).

 

[AlexJet]

On my FJC, I bought this one from Dirty Parts: http://www.dirtyparts.com/store/detail.cfm/FJ-CRUISER-DUAL-BATTERY-KIT/pid-83094

On my 40, I'm putting together my own system based on what I learned from the Dirty Parts kit (it will be similar).

Looks similar to Painless

 

[1911]

Looks similar to Painless

The Dirty Parts kit works well and was easy to install. I've had it in there for two years now and I'm still very happy with it.

 

[dwh]

I see your approach angle. I used the same methodology on wiring my 4Runner dual batteries, but they were the same type. I was told that I was wrong as if I need to winch myself then the winch will suck all the juice from Secondary and Alternator is connected to the Primary, so Secondary would be taking power not from the alternator, but from Primary which would be feeding by the engine itself. In fact I used winch once, so I don't have much experience on this side.

They told you wrong.

The alternator is supplying current to the exact same place that the secondary would be pulling power from - the positive terminal on the primary battery. So the current will flow from the alternator to that point, then divert through the battery cable to the secondary.

Not that it matters, when the batteries are tied, then it's just one big battery bank and the winch is going to draw whatever it needs from both batteries and the alternator as well.

 

[LR Max]

When I was concerned, I ran a 20 amp fuse between the two batteries. During normal operation/charging, the 20 amp fuse worked just fine, acting as a trickle charger. When winching, it did pop.

I did that for a while, then I started running my batteries in parallel. Never had a problem (until the batteries became 10 years old, but I think that was to be expected). Just do that.

Dunno, I see the prices of these complicated isolators, $400+ when done. A little fuse + everything to make it work (well done with solder, etc) can be done for under $10 with spares.

Except for water ingestion and running out of fuel, you probably aren't going to need to winch with the truck off. Also in the past, I've done a full pull with my truck off (I drive an old carb'd truck, so yes, they quit for little/no reason) of one battery and it had plenty to crank it.

 

[dwh]

A solenoid could be considered a type of isolator, but I usually think diode-based when talking about isolators. (A solenoid doesn't restrict current flow to one direction like a diode will.)

The solenoid is great for preserving the charge of your starting battery - when the truck is off, the solenoid is off and the batteries aren't linked. The issue comes when the engine is running and the batteries are in parallel / charging. One battery can suck power from another, and they are sharing the same feed off of the alternator. So unless they are in the same condition / same capacity / same state of charge, they won't be in an ideal charging situation because they are being treated (by the alternator/regulator) as one big battery instead of the two (or more) separate batteries that they really are.

A diode-type isolator doesn't change that.

Okay, yea it prevents one battery from pulling down the other, but it doesn't change how the voltage regulator behaves. The voltage regulator only sees that the voltage is either below the set voltage or not. As long as the voltage is below the set point, it keeps the alternator turned on and each battery sucks up however can overcome its internal resistance. Doesn't matter if they are the same type, age, capacity, etc.

As for one battery sucking down the other - not so much of that going on there. As long as both batteries are tied, and the secondary battery is lower, then the bus voltage will be drawn down, causing the voltage regulator to keep the alternator on. So the secondary battery is drawing from the bus. The bus has two sources of supply - the alternator and the primary battery. The alternator supply has a lower resistance than the primary battery, so almost all, if not all, of what the secondary is drawing is going to come from the alternator.

That will go on until both batteries have a surface charge equal to the voltage regulator set point and the voltage regulator turns off the alternator. After that, the secondary will drop down from surface charge faster. In that situation, the secondary could draw from the primary, but the voltage regulator is going to kick the alternator back on anyway, so it's not like the primary gets drawn down by any noticeable amount.


Batteries only need to be identical if they are tied into a permanent bank. If they are only tied during charging, then the only thing that matters is that they both require approximately the same charge voltage.

EDIT: Well, what I just said is true with a constant voltage charging system, such as a voltage-regulated alternator, or a two-stage charger (bulk/float). It's not true if using a 3-stage charger that does absorb. With a 3-stage, you don't want to mix batteries during charging.

 

[pugslyyy]

A diode-type isolator doesn't change that.

Okay, yea it prevents one battery from pulling down the other, but it doesn't change how the voltage regulator behaves. The voltage regulator only sees that the voltage is either below the set voltage or not. As long as the voltage is below the set point, it keeps the alternator turned on and each battery sucks up however can overcome its internal resistance. Doesn't matter if they are the same type, age, capacity, etc.

As for one battery sucking down the other - not so much of that going on there. As long as both batteries are tied, and the secondary battery is lower, then the bus voltage will be drawn down, causing the voltage regulator to keep the alternator on. So the secondary battery is drawing from the bus. The bus has two sources of supply - the alternator and the primary battery. The alternator supply has a lower resistance than the primary battery, so almost all, if not all, of what the secondary is drawing is going to come from the alternator.

That will go on until both batteries have a surface charge equal to the voltage regulator set point and the voltage regulator turns off the alternator. After that, the secondary will drop down from surface charge faster. In that situation, the secondary could draw from the primary, but the voltage regulator is going to kick the alternator back on anyway, so it's not like the primary gets drawn down by any noticeable amount.


Batteries only need to be identical if they are tied into a permanent bank. If they are only tied during charging, then the only thing that matters is that they both require approximately the same charge voltage.

EDIT: Well, what I just said is true with a constant voltage charging system, such as a voltage-regulated alternator, or a two-stage charger (bulk/float). It's not true if using a 3-stage charger that does absorb. With a 3-stage, you don't want to mix batteries during charging.

Ah well, I'm sure that it's just me being unlucky - my meltdown occurred while driving down the road with a basic alternator charged setup.

Still, because I had batteries smoking 2 inches below my butt I'm now a believer in having an isolator in place that will cause me to only lose one battery instead of both while charging/operating.

I was fortunate that my failure occurred on pavement where I could drive directly to an auto parts store and buy replacements - and that I was driving my Defender which has a battery shutoff switch so I could take the whole mess out-of-circuit and just operate off of the alternator until I fixed the problem. I just reached down between my legs, turned off the batteries, and kept on driving, rolled into Autozone and purchased 2 new Optimas. They do installs for free when you buy batteries so I let them - just to see how long it would take them to figure out where the batteries were.

 

[AlexJet]

Would this means I can put 2 different batteries with Painless (solenoid) system and be fine having all electrics connected to it and having secondary (smaller) as a secondary battery to boost the primary, connected when ignition ON, disconnected when ignition OFF? Or do I still need the isolator, like SurePower 13023A?
How many stages my 2000 Tacoma 3.4 v6 5VZ-FE charging system is?

 

[AlexJet]

When considering 2 batteries being the "same", what parameter is the same?
- Cold Cranking Amps
- Nominal Capacity
- Reserve Capacity
P.S. I remember 20 years ago we only looked at Nominal Capacity when were choosing the batteries...

 

[Kohburn]

even with two identical batteries, if one fails before the other it will almost always take out the other with it if not cause a fire.

one of the most simple ways to isolate them is by using a charge controller to keep the secondary battery charged. the charge controller can be fed by key switched power, and in this setup you would have all your high draw (starter/winch) power to the primary and all the low draw accessories from the secondary. and both batteries can be of any age and completely different sizes without any risk at all.

a cheap 12v solar charge controller can handle this off of switched power or have the swithed power flip a relay to turn on the charge controller.

without the need for fast discharge, cranking amps, etc the secondary battery can be a straight deep cycle.

 

[dwh]

Would this means I can put 2 different batteries with Painless (solenoid) system and be fine having all electrics connected to it and having secondary (smaller) as a secondary battery to boost the primary, connected when ignition ON, disconnected when ignition OFF? Or do I still need the isolator, like SurePower 13023A?

The purpose of an isolator is usually to allow you to put your loads on the secondary battery and drain it without having to worry about draining the primary battery - so you can still start the engine when you need to.

If the ignition is on, and the engine running, then you don't usually need a secondary battery to "boost" the primary unless maybe you've got heavy loads (like a winch) that draw more than the alternator can produce...then yea...you might want to add more battery. If that was the situation, then I'd want the secondary to be the biggest deep cycle battery I could fit.

If you just want a second battery to jump-start the truck if you happen to run the primary down and you don't use the secondary when the engine is off, then sure, you could fit a smaller battery - as long as it's big enough to jump start the truck - and just have it being charged up when the engine is running. BUT, running auxiliary loads from your primary cranking battery is probably going to kill your primary cranking battery. Cranking batteries can't handle being drained too far too many times.

How many stages my 2000 Tacoma 3.4 v6 5VZ-FE charging system is?

One. If the voltage of the system is low, the voltage regulator turns on the alternator until the system voltage comes up to whatever the voltage regulator is set to, then turns off the alternator. So charging different size batteries from that won't matter - all the batteries connected will just get charged up to the same voltage.

 

[dwh]

When considering 2 batteries being the "same", what parameter is the same?
- Cold Cranking Amps
- Nominal Capacity
- Reserve Capacity
P.S. I remember 20 years ago we only looked at Nominal Capacity when were choosing the batteries...

If the battery lists CA, CCA and RC, then it's pretty much guaranteed to be a cranking battery. A deep cycle battery will list Amp*Hours (AH) instead. Cranking batteries have lots of thin lead plates to supply heavy amps in a hurry, while deep cycle batteries have less, but thicker, lead plates to supply less amps but for a longer time.

But a cranking battery is only designed to be drained 3%...maybe 5%...every time you start the engine and then get immediately recharged. Draining cranking batteries too far will eventually kill them. With some, they might be wasted after only a few deep discharges.

Deep cycle batteries DO have CA, CCA and RC numbers - they just aren't usually listed. If a deep cycle battery did list those numbers, it would have slightly lower CA and CCA numbers than a cranking battery, and a hell of a lot more RC.

You can use a deep cycle battery as a cranking battery - it won't hurt the deep cycle battery - it just won't supply quite as many cranking amps. But you can not use a cranking battery as a deep cycle - you'll kill it.

RV/Marine batteries are usually a compromise with medium thickness plates. They can dump cranking amps faster than a deep cycle, but not a lot faster. They can handle deep discharges a little better than a cranking battery, but not as well as a true deep cycle design.

 

[dwh]

When considering 2 batteries being the "same", what parameter is the same?

And I forgot to answer your question.

The answer is: All parameters.

Age, type, size, capacity, manufacturer, factory batch/manufacture date, etc. All.

If you are going to hook up batteries into a permanent battery bank (tied full-time) then they have to all be identical or some will work harder than others.

But if you are just hooking them together when they are being charged, and it's not a 3-stage charger, then the only thing that really matters is that the batteries all want around the same charge voltage.

Ie., a flooded cranking battery and a deep cycle AGM will both be fine charging together off a 13.5v-14.4v automotive system, but a GEL battery might not be too healthy if pumped up to 14.4v. GELs are picky about voltage.

 

[AlexJet]

As I mentioned in my first post, my intentions is to use 2 Odyssey Deep Cycle batteries.
I was thinking of:

Option 1: 34/78-PC1500 (Primary) + 75/86-PC1230 (Secondary). Both batteries have Top and Side terminals.

Option 2: 34/78-PC1500 (Primary) + 25-PC1400 (Secondary). Only PC1500 has Top and Side terminals, but batteries are closer to each other on specs (see bellow).

Specs:
PC1230
- Cold Cranking Amps: 760
- Normal Cranking Amps: 870
- Reserve Capacity: 100min
- Nominal Capacity at 20hr: 55Ah
PC1400
- Cold Cranking Amps: 900
- Normal Cranking Amps: 850
- Reserve Capacity: 125min
- Nominal Capacity at 20hr: 65Ah
PC1500
- Cold Cranking Amps: 850
- Normal Cranking Amps: 1050
- Reserve Capacity: 135min
- Nominal Capacity at 20hr: 68Ah

 

[dwh]

Odysseys are nice. They are just about the only ones who make a thin plate cranking battery that is also rated for deep cycle use.

Note in the specs on the PC1500 that it can handle 400 cycles to 80% discharge. That's the lifecycle. That means you can drain it 80% 400 times and then you'll probably have to replace it. All lead-acid batteries are like that. The deeper you go, the less cycles you'll get. That same battery could probably do 3000 cycles if you only drained it 25%. You'd probably get 10,000 cycles if you only drained it 5% or less for engine starting.

If you intend to run auxiliary loads with the engine off, then you should go with a standard aux battery setup - use an isolator to charge the second battery when the engine is running, and isolate the batteries when the engine is not running. Then attach your aux loads to the aux battery so you don't drain your engine battery while running those aux loads.

For a winch, I would hook the winch up to the engine battery to supply heavy amps under load, and allow the aux battery to help out as needed. The engine will probably be running in that situation so the alternator will help out as well. (Well...I would with normal batteries. With Odysseys, it probably doesn't matter which battery you hook the winch up to as long as the battery cables between them are heavy enough to handle the amps.)

All other aux loads should go to the aux battery.


If you hook up your aux loads to the engine battery and run it down, then the aux battery is basically useless except to maybe jump start the truck when you need to, and to help out when running the winch.

As far as charging, the only difference in those batteries you listed is the capacity. They all accept exactly the same charge parameters. The charging specs are described in the Odyssey Tech Manual:

http://www.odysseybatteries.com/files/US-ODY-TM-001_0411_000.pdf

In other words, with those Odysseys, being charged from a vehicle's charging system, you can mix and match them to your heart's content.


Also, keep in mind that even 68 amp*hours is not a hell of a lot when talking about running aux loads for days while camping. If you want a lot of cycles (long life) from those expensive batteries, then don't drain them below 50% - which means that you'd actually have 34ah available.