Parallel Batteries

[pointblank5]

Is there anything wrong with simply buying two identical batteries, using one to replace the original starting battery in the car, and putting one in the tray, and joining the two in parallel with some nice thick cable?

no isolators, relays or whatever, maybe just some nice big fuses incase the cables got damged etc.

this would just serve to double the Ah and ccA ratings wouldnt it?

thanks for any help, cant seem to find a reliable informed answer on the net...

cheers, James

 

[ONLOCK]

nothing wrong with doing that mate but honestly for the 95 bucks for a redarc isolator why not seperate them, only plus with what your doing is that you can run your winch longer without the battery going flat.

 

[reel-sensation]

Hi

I build camper trailers and that is the way we put the two batteries in. Works fine!
Alan

 

[justdrinkbeer]

you'll want some big arsed cables, i'd buy weld flex about 95sq mm, plus you can still flatten them both, will just take longer, go the isolator

 

[tweak'e]

Is there anything wrong with simply buying two identical batteries, using one to replace the original starting battery in the car, and putting one in the tray, and joining the two in parallel with some nice thick cable?

no isolators, relays or whatever, maybe just some nice big fuses incase the cables got damged etc.

this would just serve to double the Ah and ccA ratings wouldnt it?

thanks for any help, cant seem to find a reliable informed answer on the net...

cheers, James

quite common. in fact i'm doing the opposite in my toyota...getting rid of the 2nd battery.

two problems.
you need a really big cable because of the distance and that both are being used to start the battery. any differences in discharging the batteries often ends up stuffing up the batteries. so if its a long run and small cable one battery will discharge more than the other. also means no running gear directly off the 2nd battery.

the other thing is that when one battery dies the other often goes with it.
you have to treat both as one, so double the cost.

its better to separate them so only one gets used for starting and it means you can run other stuff off the 2nd.

 

[Old.Tony]

I think the motivation is right but the distance is too much. I'd seriously look at the isolator as well, and use a decent sized cable (6 sqmm or 8 sqmm) with a fuse on each end.

 

[tommy222220_0]

Is there anything wrong with simply buying two identical batteries, using one to replace the original starting battery in the car, and putting one in the tray, and joining the two in parallel with some nice thick cable?

Should be fine. Depending on use, an isolator isn't needed but a fuse at each end reccomended.

As for cable size, the std alternator puts out 60A (max) shared between both batteries so 8 gauge cable should be fine.

But if you are using it to extend your winching time, they can draw above 400amps! Unless you can reduce the distance between your batterys, your looking at 2 or 0 gauge.

 

[pointblank5]

thanks for all the help fellas!!
I dont actually have a winch, but i have a fairly substantial sound system
I like to run the sound system while the car is off for a while sometimes, and I really cant be arsed to convert the whole thing to run off an isolated second battery.
So extending the run time without discharging the pair of batteries too much is attractive to me.

As for the isolator, I dont really run that many accessories... maybe 2 led work lights and the fridge. The standard battery handles that fine overnight when camping.

So the general consensus is that aslong as the cable is thick enough (is 2 or 0 gauge enough?) then I should be right?

I also read that some people reckon because of the slight voltage drop of the joining cable, the batteries can see each other as a load when trying to equalise their voltages, and equalise down to nothing over time if left?

Cheers, James

 

[tommy222220_0]

I also read that some people reckon because of the slight voltage drop of the joining cable, the batteries can see each other as a load when trying to equalise their voltages, and equalise down to nothing over time if left?

Voltage drop is a function of current. If you have a large current (with small wire) you will get some significant V drop, but if there is no current V drop is nothing.

Auto Cable by Collyn Rivers

Batteries will slowly discharge on thier own if left sitting idle for a while (months)

 

[Leprechaun]

I'm sorry, but I can't believe anyone would contemplate wiring their batteries this way.

Other than a comp truck or a Kenworth.

 

[4.8GU]

Yeah I have to agree. It is not smart. You are going to buy a second battery anyway so just get a decent one to suit. Optima comes to mind but I am sure there are plenty of other options.
Seen plenty of start batteries with 800cca or more and decent a/h times.

Remember that, while the batteries will take longer to discharge in your proposed set up, they will also take much longer to charge due to the size increase. Once they are flat you are screwed. Also the cable run is a killer. With any sort of voltage drop you would get far decreased performance as one battery would drag the other down trying to equalize.

Find another way imo

 

[Leprechaun]

I'm sorry, but I can't believe anyone would contemplate wiring their batteries this way.

Other than a comp truck or a Kenworth.

Wait a minute, what a dumb ass, aren't 2.5 D22 wired in parallel???

 

[tweak'e]

Wait a minute, what a dumb ass, aren't 2.5 D22 wired in parallel???

yes, a lot of vehicles come factory fitted with duals batteries in parallel (eg my toyota). but all that i've seen are under the bonnet, not with one way back in the tray.

 

[heata]

Wait a minute, what a dumb ass, aren't 2.5 D22 wired in parallel???

I dont know if it is all 2.5s I think it is from 2009 onwards? but maybe someone can confirm?

 

[pointblank5]

Ok thanks for the help guys, so theres mixed responses whether to do this or not...
4.8 GU, are u saying that I should get an upgraded battery and stick to single battery setup? I have seen the yellow top start/deep cycle batteries advertised... could one of these be the go? And does anyone know if these are heavier/lighter than a similar cranking battery?

I think i'd be happy just having a larger capacity single battery, but i dont want to add too much extra weight up front or change the battery tray size.

Thanks in advance for your replies, James

 

[mitch92]

For the price and for what it does i would seriously recommend getting a redarc or similar if running two (or more) batteries. You can still over-ride the redarc if needed so still have 2 batteries in parallel, but much better set-up.

 

[Old.Tony]

If this is to run a high-powered stereo system in the cabin, I'd look at a Redarc isolator and a second battery in the tub, and run the system exclusively from the second battery.

The day you flatten that thing while camping in the middle of nowhere and are still able to start your car and drive off will be the day you'll count your blessings.

 

[Red Dog]

I used to have a parralell set up from main battery to deep cycle in the tray, however it ended up shagging my deep cycle.
My current set up involves a Matson controller between the batteries which so far has caused no issues as the batteries disconnect from each other once the engine stops. The Matson also has a switch on ot so the batteries can be manually connected if required.

 

[pointblank5]

Thanks again guys, I'm needing all the help i can get on this topic LOL

Ok, how about this idea then...
replace my starting battery with a d.cycle/cranking rated battery.
move my original cranker to the tray.
use a solenoid between the two batteries, wired so with ignition ON the batteries are parrallel (so they crank and charge together)
with ignition OFF, the batteries are separate (so i can run the d.cycle/starter flat, but still have a charged cranking battery ready to supply power when i turn the key)

I realise I'll have to use decent cables to allow enough current to come from the rear battery.

Does this sound feasable or completely stupid?

 

[Old.Tony]

It sounds fair, but I'd leave the cranking battery up front so you aren't shunting that much current up from the back. The isolator is a good idea, but I'd not get the auxiliary battery to do any cranking - just leave that for your starter.