Dual Battery setup - proposed

[gigy]

Hi all,
I am planning to put in a second battery in to my baleno for two purpose.
i have just now downgraded the battery to default capacity from the large one previously installed. with my modest ice setup there was no issue previously but with new one the car lights also thump along with music, this was not there previously. so i guess need more reserve capacity. ideally the second one needs to be near the amplifier but i am putting into the stock tray itself as of now.
Second reason i can use this as a emergency backup built in. in case the primary battery drains of due any reason (since it always remains connected) i can use the second anytime to start the car.( it connects to car only when powered)
One of my friend is running a dual setup with complicated electronic control and voltage indication and all but i want to keep the system simple. there is no issue in his car due to doubling of battery capacity .
Please suggest improvements
i got some free time now, thats why this time pass.
A diagram of setup below.

[low_bass_makker]

What size of contactor or relay you plan to use ?

[gigy]

I have this contactor/relay lying around for sometime without use. plan to use it.
Its specification
Mobile Audio Relay and Battery Isolator
Great for isolating a second batter making it dedicated to the stereo system
Does not create a voltage drop to the second battery like conventional isolators
80 Amps at 12V Continuous Power Handling
150 Amps Surge Power Handling
Switching Power: 10 - 16 VDC
Draws Less Than 1 Amp When On
Dimensions: 2-11/16" L x 3-5/16" W x 4" H.

I hope it can take few starting current cycles in its life time.

[BaCkSeAtDrIVeR]

You may need to upgrade the alternator so that the 2nd battery is charged properly.

[gigy]

We have another baleno running for ,more than 2 years now with two batteries and there is no issue till date regarding his car electrical system.
Even he has a basic ice setup like mine and his dual battery did save him few time from being stranded on road.
Basically the second one will always be in a charged state from day one. it will be the primary one which will have a larger charge/discharge graph, so don't expect trouble.

[karankapoor]

For the reason stated by you i don't think one needs 2 batteries in a car for at least a normal ICE with 1/2 amplifiers which require 60/80 amp current and for the second reason i personally dint faced any problem in the past 17/18 years of my driving, But if you want 2 off them in your car go ahead but be sure you are clear with every thing before you install the second battery.

[gigy]

Even i didn't expect any change coming when i was replacing the previous 48 one with this 35amph one, but the thing is the power fluctuation now exists. nothing else has changed, its the same amp, wiring player, groundings etc. so what could be the issue. Even i dont know if this is going to help

[karankapoor]

Why had you changed the battery with a 35 ampere battery this is actually a downgrade any particular reason, I think this is causing dimming.

Baleno needs a 45 amp battery or a 35 amp battery ?

[gigy]

The stock one is 35amp battery. i had installed the 48 amp one earlier.

[Ravveendrra]

Why did you shift back to 35A from 48A? It will be much easier, cheaper and uncomplicated to upgrade your battery and use only one battery.

Cheers,

[gigy]

When we were replacing batteries, i took one large battery and my friend put in two smaller batteries. in due course of use i had problems regarding total voltage in car, had to replace alternator, his setup is running fine till date with 70amph in total. so the dual battery had bitten me long ago and i was waiting for present one to go bad. with this big one there was no place to put in a second one. didn't want to put it in boot. when time came i have gone for stock one as two sit in tray easily with minor modification.

Now earlier plan was to stagger purchase of second one by a year so that both don't loose service life together but with dimming of lights in night i have changed plans to put in same or higher life one but of same capacity,same or different brand.

[pranava999]

Have you considered the big 3 upgrade? Do look into it. I think the upgrade could be an alternative to having another battery on-board.

[low_bass_makker]

I am using two batteries for quite sometime now. First of all you will need to watch the voltage as the alternator will have to work double for charging the two batteries. Rest no need to put the contactor or any thing if both the batteries are same and new there will be no issue. And yes with one battery close to the amps make them play better.

[gigy]

Contactor is actually to see that only one battery is involved in the starting of car and dont get discharged along with the main one in case i forget switching off headlights in parking.(it happened twice with me). This will also ensure that alternator will have to charge back only one battery at higher current. the second is doing a job more like a capacitor. To place it in boot i will have to put in a fuse which will have to take the starting current load also, so its not practically safe i suppose. if it was to support the amplifier only a 60amp fuse would have done the job.
I have left with two wires to be replaced/supported( battery to ground, alternator to battery, it was to happen with the install. Will do this first and see if it is making a difference before buying the second battery.

[DerAlte]

Perhaps you could consider a diode in parallel with the contactor main contacts. Anode to main battery +, hence it will charge when the main battery charges. Cathode to the +ive of the 2nd battery. The contactor contact will be, at this time in Open position. Because of the diode, no current will be drawn from the 2nd battery during cranking.

Now, when you want to use the 2nd battery for cranking, 'make' the contact and it will short the diode and bypass it. In this state, the 2nd battery will supply the juice to crank the engine.

Anyhow, if the alternator (due to to poor current regulation) & 2nd battery combo cannot supply the current needed by you ICE dynamically, the lights will still dim in sync with large current demands.