Connecting a Second Battery

[Sharp_Shoota 10+ year member]

Ok So I've already baught a bigger alternator so i fugred might as well go all out and connect a second battery.

At first I thought do i just connect the second battery to the first one as the alt would fill the new battery then when thats full fill the second?

Or would I connect both batterys straight the alt?

Realize this might be a stupid question but wanted to check Ime doing this right.

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[Diplexers 10+ year member]

What you need to get is a battery isolator, it lets you run two batteries, but you can wire one battery to the stereo system and the other one to the car electrical functions. The stereo can't drain the car battery and tha car battery can't drain the stereo battery.

 

[ngsm13 5,000+ posts]

Battery isolator is a waste of money. I know, along with many other EXTREMELY experienced caraudio vets that informed me it's a waste. All you need to do is connect a fuse wired to the pos. on the front batt. and run it to the pos. on the rear batt. Then ground the rear batt. in the rear. This is how mine is done...no problems at all...and i get bout 14.1v at both batts. peace

NG

 

[helotaxi 5,000+ posts]

Battery isolator is a waste of money. I know, along with many other EXTREMELY experienced caraudio vets that informed me it's a waste. All you need to do is connect a fuse wired to the pos. on the front batt. and run it to the pos. on the rear batt. Then ground the rear batt. in the rear. This is how mine is done...no problems at all...and i get bout 14.1v at both batts. peace
NG

As long as the batteries are identical then you don't need an isolator. If you are running different batteries front and rear then a charging relay is a good idea. It allows the batteries to run in parallel when the car is running but isolates the two batteries when engine is off. This serves three functions: 1) it allows the alt to charge both batteries when the car is running and the alt is the primary source of current. 2) It keeps the two batteries from trying to equalize when the engine is off which would lead to the premature demise of one or both batteries. 3) It keeps you from draining the starting battery when you are running the system with the car off.

 

[lumpmoron2 10+ year member]

This topic comes up so often with people hearing different stories from everyone. i've heard yes & no you dont need a battery isolator. from personal experience i dont use a battery isolator for 2 of my aux batts. isolators are a waste of money and time because the can damage your batts when you start your car, causing an arc of current when the 2 batteries connect from the isolator. its true the aux batts with lose power from the amp first since its closer to the amplifer pulling all the power. when the car is running it will mostly be using the alt anyway. when you turn the car off both batts will even out the voltage between eachother and things will return normal. having an aux batt in the rear will help things out only IF your alt can power both of them AND still power your amplifer when the car is on. theres more technical mumbo jumbo but i just dont care to use battery isolators and i've run mutiple batteries for a long time. :thumbsup

 

[helotaxi 5,000+ posts]

true the aux batts with lose power from the amp first since its closer to the amplifer pulling all the power

BS in the grand scheme of things. If your system is wired with adequate size cable the resistance of the wire going from the main battery to the AUX battery will be all but unmeasurable. Any difference in voltage between the two batteries will equalize almost instantly.

. when you turn the car off both batts will even out the voltage between eachother and things will return normal

Which can damage batteries if they are not the same brand and model.

having an aux batt in the rear will help things out only IF your alt can power both of them AND still power your amplifer when the car is on

How do you "power" a battery? A battery is a current SOURCE. You might need to recharge it but two or twenty batteries will take the same amount of current to recharge as only one given the same total initial current draw and time. Adding an extra battery will not hurt a system. I agree that it will not FIX an inadequate charging system, only a HO alternator can do that, but it will not hurt.

because the can damage your batts when you start your car, causing an arc of current when the 2 batteries connect from the isolator

This is basically what happens every time your battery goes from discharge to charge anyway, you know like when you start your car. You are not going to damage the battery by using an isolator, regulator or relay. The contacts on the isolators have a service life, though. They do arc a bit and after awhile the contacts can pit and corrode and no tlonger give a good connection. Relays are relatively cheap, though, and it won't break the bank to have to replace one every year or so.

 

[Trixter 10+ year member]

I have ran dual battery set ups for about 9 years now. I have never used anything to seperate them. I have used batteries of different sizes (same brand though). I have never had any problems. Connect the 2 pos and ground each neg. It's a good idea to put a fuse of even a fused link at BOTH pos incase somethin happends to the cable in between them. If you have a system that really needs two batteries, then chances are you shouldn't be playing you system without the car running anyways.

 

[Diplexers 10+ year member]

Look, since you already have the HO alternator you might as well get the isolator. Its just nice to have in case you have any problems with one battery it won't effect the other one; call it better safe than sorry. As for those who don't run isolators, more power to ya, its not my style, I'll stick with the isolator. Plus as I said earlier, you can play your stereo with the car off with out worrying about killing the cars battery. Piece of mind.

 

[Trixter 10+ year member]

The only reason I don't use anything is because I need all the power I can get. I want the power of both batteries and not just one. I don't know his situation, but in mine, there is no way I would even think about running my system with out the car running. If I were to use an isolator and play my system with out the car running, the single battery that would be powering it would be dead at the first bass note. Even if I used two batteries with out the car running they both would be dead by the time the second bass note would hit. It all depends on the situation.

 

[lumpmoron2 10+ year member]

Trixter has another point. I cant run my system without my car on either since it draws so many amps. an isolator is just another thing that would cost money, get in the way, and probably piss me off.

 

[ngsm13 5,000+ posts]

Trixter has another point. I cant run my system without my car on either since it draws so many amps. an isolator is just another thing that would cost money, get in the way, and probably piss me off.

VERY true....so, if u actually have a system that pulls enough current to warrant a HO alt and an extra battery...then you'd want as much current available as you can get...so DO NOT WASTE money on an isolator. True caraudio specialists that know what they're doing don't use them...peace

NG

 

[Trixter 10+ year member]

Finally the light has been seen.//content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

 

[Sharp_Shoota 10+ year member]

Heh thanks for ur input guys, think ive decided not to bother with a second battery. Will just have to be more carefull and make sure the engines runnings when I got the system on.