**Dual Batteries**

[MOABICON]

If I run dual batteries in my 03 TJ 4.0, do they both
have to be the same>" Cold Cranking Amps"?

[4Banger_madness]

it would be recommended and at our shop we always put two new batteries in at the same time or the older one can drain the new one

[Nootch]

you SHOULD have the same batteries hooked up under hood.  I forget the specifics on why an older battery can "kill" a newer one, but it basically has to do with how the alt pushes and the batteries divide the power. 

But i now must ask WHY you are needing two batteries.  Mayhaps you just need a better alternator for your application.

[binare]

you SHOULD have the same batteries hooked up under hood.  I forget the specifics on why an older battery can "kill" a newer one, but it basically has to do with how the alt pushes and the batteries divide the power. 

But i now must ask WHY you are needing two batteries.  Mayhaps you just need a better alternator for your application.

X2 better alternator will your battery recover faster then the extra reserve from 2 batteries will for things like winching. General rule of thumb is dual batteries for vehicle NOT running, better alternator for vehicle running.

[w squared]

I'll chime in with the rest of the folks here and suggest that you "match" both age and type when you put in dual batteries. This means that they'll charge evenly as a pair, and discharge evenly as a pair.

[Vinman]

When I get around to adding an additional battery to my jeep I plan on keeping it 100% isolated from the main battery. I will use a marine battery switch and simply switch between to two batteries when required.
By doing this I am accomplishing a few things.
-  I will not have to worry about running down the battery when the jeep is not running and being left stranded
-  It will add no additional load on the alternator trying to charge both batteries at once
-  Neither battery will effect the other (no need to match size, type or age of batteries)
- I will still have the ability to boost myself in the event I do drain the main battery
- In extreme winching scenerios, I can set the switch to select both batteries at once

The plan is to run the battery cables from the jeep directly to the battery switch and then connect both batteries directly to the other side of the  switch. By wiring this way, there will bo no primary and no secondary battery, both will have the ability to be primary and secondary batteries.
Of course, doing it this way does require occasionally manually switching between both batteries to ensure they both maintain a charge. I'll just get in the habit of switching once a week.
 
A quick search for a switch turned up this: http://www.iboats.com/Perko-Heavy-Duty-Battery-Selector-Switch/dm/cart_id.852907845--session_id.779530475--view_id.5377

Vince

[MOABICON]

Thanks for the feedback. I've read about
it somewhere but, just forgot. Just was
thinking about it. 

[w squared]

Vinman, you may want to be careful with using a true marine deep-cycle battery for short-term high-load applications like winching and starting the vehicle. I don't have any specific, but I've heard that using a deep cycle for "burst" applications can have the same sort of effect on the battery as using a normal starting battery for a deep-cycle type application (premature battery failure)

I definitely like your idea about isolating the batteries from each other if you're not going to exactly match type and age. Makes perfect sense.

[Vinman]

Vinman, you may want to be careful with using a true marine deep-cycle battery for short-term high-load applications like winching and starting the vehicle. I don't have any specific, but I've heard that using a deep cycle for "burst" applications can have the same sort of effect on the battery as using a normal starting battery for a deep-cycle type application (premature battery failure)

I definitely like your idea about isolating the batteries from each other if you're not going to exactly match type and age. Makes perfect sense.

I think you misunderstood slightly, I am not using a marine battery, just a marine dual battery switch.
I quickly found the switch I linked to but I will have to do a bit more research and make sure the switch can handle the load of the winch under hard use.

Vince

[Greg-100]

I ran ambulances for 30 years, they can have up to 4 batteries in them, so have a little bit of experience.

You can mix and match and not have any big problems, just small issues.

The isolator acts as a one way valve, as in power goes into the battery from the alternator but can not be drained out by another battery in the system on the charging side. But if the output side is not separate, then one battery will drain the other.

You wire the output of one battery to the winch only(key word is only, can not share any power to OEM side) and manually boost from battery one to battery two if needed.

Or have a battery switch or relays for the output side of the power from the batteries.

Battery one feeds the normal power for the jeep, battery two feeds the winch etc.

With the switch or relays you can have one battery boost the other or run independent of each other.

The alternator senses a voltage drop and increases voltage/amps output till the voltage comes back up to the trigger voltage of the alternator.

So the problem with a mix and match battery system is if one battery is low then all the batteries are being charged till the low battery is charged or if one battery is a higher rated battery, then the lower rated battery is charged first and is still being charged till the higher rated battery is charged.

But in real life it is not a big issue, alot of ambulances have two full sized batteries to run the OEM in the front and smaller batteries in the back due to the space issues.

In the jeeps the alternator is being overworked when you add bigger batteries and / or winches etc. Once in awhile is not an issue, but heavy winching, lots of high output lights will shorten the life of the alternator.

Greg

[JohnB]

They do not need to be matching batteries if they are properly isolated from each other, which they should be regardless...

[Nootch]

    +   


more than enough capacity and draw, and more than enough charge.

[Vinman]

    +   


more than enough capacity and draw, and more than enough charge.

Good luck with newer Optimas, I haven't heard amything good about them in years.

[Nootch]

i think its mainly in the D34 model of Optima ( the every day car one) the one pictured is a D31A which is industrial sized.  mine was a used member that got "killed" from a frac unit and its been flawless since i charged it.