everstart battery in the back?

[KaeZoo 10+ year member]

So I think we can agree that any time the alternator is NOT being taxed, the extra battery serves no purpose, right?

And I think we can probably agree that for most people, the alternator is not normally going to be overloaded very often for normal music listening. There are people out there who have are listening to their system at its maximum output at all times, but I suspect they're in the minority.

The question is, how much help does a second battery really provide during those peaks when the alternator can't handle the current demand? Will it really make an audible difference in the sound?

So let's assume we have a system with a single Optima starting battery under the hood, no second battery, and trunk-mounted amplifiers wired with a 15' run of 1/0 wire. Let's pretend that our system suddenly requires an additional 200 amps of current beyond what the alternator can provide (a bit of a stretch for the type of systems we're talking about, but hey, we like it loud). The alternator has overloaded, the system voltage drops and now 200 extra amps of current has to come from the battery.

The Optima Red Top has an internal resistance of .0030 ohms. Our 1/0 wire has a resistance of .0001 ohms/foot, so its total resistance is .0015 ohms. That gives us a total resistance of .0045 ohms that our 200 amps has to come through, giving us a voltage drop of 0.9 volts.

Compare that to the same system with an additional Optima deep cycle battery in the back. For simplicity's sake we'll assume there's no resistance between the second battery and the amplifier terminals. Yellow Top internal resistances vary with different models, but .003 seems to be about average. Now our current load can be split between both batteries, so the Yellow Top needs to provide only about 100 amps, leading to a voltage drop of .3v. (We'd probably get a bit more voltage drop if we really factored in the load on the Red Top battery through the wire, but .3v of drop is definitely the best-case result).

So in this example we've got end up with a voltage difference of .6 volts between a second battery and only one battery. That might make a measurable difference in output, but it's very arguable whether it would make an audible difference. And when you do that math with a less extreme current demand, there's less of a difference between the two systems. How often, in a non-SPL system, would you expect a current demand of 200 amps above the alternator's capacity?

When you factor in the extra cost and weight of a second battery and wiring, as well as the extra load on the alternator (you can argue how much current is required, but clearly two batteries make more work for the alternator than just one battery) I really can't see the benefit of additional batteries in most systems.

 

[aaronmiiller 10+ year member]

In MOST systems, i completely agree with you kaezoo, but you have got to be the first person ive ever heard say that a second battery in the rear will actually hurt you. The second battery might make your alt strain a little more than usual, yes, but with the second battery, you have the protection of having the voltage right next to the amp, when the amp needs it.

 

[audiolife 5,000+ posts]

So I think we can agree that any time the alternator is NOT being taxed, the extra battery serves no purpose, right?
And I think we can probably agree that for most people, the alternator is not normally going to be overloaded very often for normal music listening. There are people out there who have are listening to their system at its maximum output at all times, but I suspect they're in the minority.

The question is, how much help does a second battery really provide during those peaks when the alternator can't handle the current demand? Will it really make an audible difference in the sound?

So let's assume we have a system with a single Optima starting battery under the hood, no second battery, and trunk-mounted amplifiers wired with a 15' run of 1/0 wire. Let's pretend that our system suddenly requires an additional 200 amps of current beyond what the alternator can provide (a bit of a stretch for the type of systems we're talking about, but hey, we like it loud). The alternator has overloaded, the system voltage drops and now 200 extra amps of current has to come from the battery.

The Optima Red Top has an internal resistance of .0030 ohms. Our 1/0 wire has a resistance of .0001 ohms/foot, so its total resistance is .0015 ohms. That gives us a total resistance of .0045 ohms that our 200 amps has to come through, giving us a voltage drop of 0.9 volts.

Compare that to the same system with an additional Optima deep cycle battery in the back. For simplicity's sake we'll assume there's no resistance between the second battery and the amplifier terminals. Yellow Top internal resistances vary with different models, but .003 seems to be about average. Now our current load can be split between both batteries, so the Yellow Top needs to provide only about 100 amps, leading to a voltage drop of .3v. (We'd probably get a bit more voltage drop if we really factored in the load on the Red Top battery through the wire, but .3v of drop is definitely the best-case result).

So in this example we've got end up with a voltage difference of .6 volts between a second battery and only one battery. That might make a measurable difference in output, but it's very arguable whether it would make an audible difference. And when you do that math with a less extreme current demand, there's less of a difference between the two systems. How often, in a non-SPL system, would you expect a current demand of 200 amps above the alternator's capacity?

When you factor in the extra cost and weight of a second battery and wiring, as well as the extra load on the alternator (you can argue how much current is required, but clearly two batteries make more work for the alternator than just one battery) I really can't see the benefit of additional batteries in most systems.

an alt can be slow in reacting do to the voltage regulator and reguardless it always reacts to the load. an alt isnt always 200 amps either as it puts out what it can (rpm dependent) and only puts out what it needs. clearly more work? so are you saying to use bad batteries or are you saying that the batteries will actually get used enough with the car running to require alot of draw? batteries arent always wanting a huge amount of current and if they were that inefficient then they wouldnt hold a charge long enough to go a few days without being started. a good battery of today can go SEVERAL months without a charge and STILL start the car. now my arguement isnt that the battery is the main source but in a typical car a high output alt does 50-60% of its power at idle. you can change pullies heck you can even up your idle(all will increase wear) but point being is if you ACTUALLY need a 200-300 amp alt somewhere along the lines when you have your system up and you are at idle it will more than likely be getting at least some help from the battery at some point and thus helps put the brakes on as far as how far the voltage will drop.

 

[KaeZoo 10+ year member]

In MOST systems, i completely agree with you kaezoo, but you have got to be the first person ive ever heard say that a second battery in the rear will actually hurt you. The second battery might make your alt strain a little more than usual, yes, but with the second battery, you have the protection of having the voltage right next to the amp, when the amp needs it.

I'm not the first. David Navone and Richard Clark put together a little demo back in the mid '90's where they hooked up an alternator to an exercise bike and had people pedal it to power a system. Then they kept adding batteries until it became impossible to pedal the bike. It's detailed in the Nov 94 issue of their Autosound 2000 Tech Briefs.

Anyway, I'm not sure why it's considered that much of a benefit to have the voltage "right next to" the system. There's no time or distance constant in Ohm's Law; a current load at any part of the circuit will affect every part of the circuit, instantly. The only factor to consider is the resistance in the wire between the battery and the amplifier, and for big wire the actual resistance doesn't add up to much. Again, distance doesn't matter, only resistance matters; a amplifier will get the power it needs just as quickly from the battery under the hood as from a battery right next to it. There is no delay, just a minor voltage drop that isn't audible unless the wire is much too small. And the same resistance is present when the alternator (the real power source for the system) has to recharge the second battery.

It all comes down to extra cost, extra work, and extra load on the alternator, in exchange for a boost in voltage that won't be audible in almost any system.

 

[aaron7114 10+ year member]

I'm not really worried if there is an audible difference or not. I just want to keep my amp from going into protect due to low voltage.

 

[KaeZoo 10+ year member]

an alt can be slow in reacting do to the voltage regulator and reguardless it always reacts to the load. an alt isnt always 200 amps either as it puts out what it can (rpm dependent) and only puts out what it needs.

Granted, and that's when the battery picks up the slack. But I've yet to see anything that shows two good batteries make an AUDIBLE difference compared to one good battery. We're not talking about SPL measurements, we're talking about what you're going to hear and notice when you're listening to your system.

clearly more work? so are you saying to use bad batteries or are you saying that the batteries will actually get used enough with the car running to require alot of draw?

I'm saying that two batteries will clearly present a bigger load to the alternator than one battery. You can argue about how much load they present, but even fully charged they're not invisible to the alternator. They require some current and it's obvious (or it ought to be obvious) that two require more than one.

batteries arent always wanting a huge amount of current and if they were that inefficient then they wouldnt hold a charge long enough to go a few days without being started. a good battery of today can go SEVERAL months without a charge and STILL start the car. now my arguement isnt that the battery is the main source but in a typical car a high output alt does 50-60% of its power at idle.

All the more reason not to put an unnecessary extra load on the alternator. Every amp used by the battery is one less for the system; if the alternator's can't even supply its maximum output then you're just drawing from the battery that much sooner...then its up to the alternator to recharge it again.

you can change pullies heck you can even up your idle(all will increase wear) but point being is if you ACTUALLY need a 200-300 amp alt somewhere along the lines when you have your system up and you are at idle it will more than likely be getting at least some help from the battery at some point and thus helps put the brakes on as far as how far the voltage will drop.

Nobody's arguing against batteries; nobody's even arguing against upgrade batteries. I'm just arguing against throwing in a second battery when one battery can handle the extra demand without a problem, even in a high power system.

 

[audiolife 5,000+ posts]

I'm not the first. David Navone and Richard Clark put together a little demo back in the mid '90's where they hooked up an alternator to an exercise bike and had people pedal it to power a system. Then they kept adding batteries until it became impossible to pedal the bike. It's detailed in the Nov 94 issue of their Autosound 2000 Tech Briefs.
Anyway, I'm not sure why it's considered that much of a benefit to have the voltage "right next to" the system. There's no time or distance constant in Ohm's Law; a current load at any part of the circuit will affect every part of the circuit, instantly. The only factor to consider is the resistance in the wire between the battery and the amplifier, and for big wire the actual resistance doesn't add up to much. Again, distance doesn't matter, only resistance matters; a amplifier will get the power it needs just as quickly from the battery under the hood as from a battery right next to it. There is no delay, just a minor voltage drop that isn't audible unless the wire is much too small. And the same resistance is present when the alternator (the real power source for the system) has to recharge the second battery.

It all comes down to extra cost, extra work, and extra load on the alternator, in exchange for a boost in voltage that won't be audible in almost any system.

i never talked about adding alot of batteries or keep adding batteries to cover up the sort commings of said electrical system...the alt will turn harder due to the actual load (not just the batteries) and it does take time for an alternator to react. from load placed to power output. most of it is dependant on the voltage regulator. never said the alt wasnt the power source when the car is on but the battery is its back bone. the car electrical system by design works the way it does and at a point well before you get to 12.5v the battery is starting to help. i have also had a 2000+(all ppi pm series) watt system run on a 90 amp alt (was later changed to a 120 dual output) but oddly enough when the alt belt would scream when the system was turned up was when it wasnt hooked up to the rear battery....hmmm also power goes considering car amps were designed to work inbetween a range 11-15v usually and the output difference to the human ear between 12.5v and 14.4 would be inaudiable as well. might meter you .4 db more ... if you cruise the town with friends and park and someone wants to "hear" your system what do you do? say "let me rev up to 2k rpm"? or "ok let me start up my car"? if you go to db drag unless you are in extreme class or super street the car is OFF you go to a sound off for sq again your engine is off. i have ran second batteries in most of my cars NEVER had an issue. only issue i can ever recall happening though delt with a high output alt and a starter battery only set up:laugh: .......

 

[audiolife 5,000+ posts]

Granted, and that's when the battery picks up the slack. But I've yet to see anything that shows two good batteries make an AUDIBLE difference compared to one good battery. We're not talking about SPL measurements, we're talking about what you're going to hear and notice when you're listening to your system.

if you are running 1 battery under the hood FACTORY sized you are putting more duty on that battery. its not just working for the audio system its working for the whole car. stereo cranked, up rolling down windows, fan, AC .....

I'm saying that two batteries will clearly present a bigger load to the alternator than one battery. You can argue about how much load they present, but even fully charged they're not invisible to the alternator. They require some current and it's obvious (or it ought to be obvious) that two require more than one.

if i have 2 batteries 1 has 4x the load of the other which is going to be better? besides that an audio system isnt going to be a constant ultra heavy load on an alt when playing normal music. if you dont listen to a system cranked up 100% of the time with an inadequate alt the second battery will do what its suppost too in covering the holes presented by low rpm jammin or flat out tone blasts with the satisfaction of knowing you can listen to it with the engine off as well

All the more reason not to put an unnecessary extra load on the alternator. Every amp used by the battery is one less for the system; if the alternator's can't even supply its maximum output then you're just drawing from the battery that much sooner...then its up to the alternator to recharge it again.

by the time you are overloading the alt out the battery is helping or do you actually believe an alt at rated power is at 14.4v? i wont argue that the point it starts to fall doesnt change (for the worse) but it is more than made up for by what the battery holds at a greater time of need. plus if your alt has trouble keeping a battery or 2 batteries charged ITS TOO SMALL.

Nobody's arguing against batteries; nobody's even arguing against upgrade batteries. I'm just arguing against throwing in a second battery when one battery can handle the extra demand without a problem, even in a high power system.

i used to think that way ........ only cost me a top 5 spot at world finals back when they were alot of competitors and large crowds that attended....//content.invisioncic.com/y282845/emoticons/blackeye.gif.66a1670f5aaf7f406e783a63e3387dc5.gif

 

[KaeZoo 10+ year member]

if you are running 1 battery under the hood FACTORY sized you are putting more duty on that battery. its not just working for the audio system its working for the whole car. stereo cranked, up rolling down windows, fan, AC .....

Why are we limited to FACTORY sized? I haven't been comparing upgrade batteries to stock batteries at all. What I've said from the start is that if you have the right battery under the hood, adding a second battery in the trunk doesn't serve a useful purpose for a system that's mostly used with the engine running.

if i have 2 batteries 1 has 4x the load of the other which is going to be better? besides that an audio system isnt going to be a constant ultra heavy load on an alt when playing normal music. if you dont listen to a system cranked up 100% of the time with an inadequate alt the second battery will do what its suppost too in covering the holes presented by low rpm jammin or flat out tone blasts with the satisfaction of knowing you can listen to it with the engine off as well

I'm not sure what your point is with the 2 batteries, one with 4x the load of the other. Again, I'm not comparing one battery vs. a replacement battery! I'm saying a battery is a load on the alternator, and if you add another battery, you have a bigger load on the alternator. The current demands of one battery vs. another aren't relevant; the point is that whatever the demand is, adding another battery can only increase it. You can certainly say that the extra load isn't very much; fine, I won't argue about it. But what you can't say is that adding a second battery results in less load on the alternator, or an unchanged load on the alternator.

by the time you are overloading the alt out the battery is helping or do you actually believe an alt at rated power is at 14.4v? i wont argue that the point it starts to fall doesnt change (for the worse) but it is more than made up for by what the battery holds at a greater time of need. plus if your alt has trouble keeping a battery or 2 batteries charged ITS TOO SMALL.

By the time you are overloading the battery is helping, but that doesn't mean it's reducing the load on the alternator. The instant that the alternator recovers to the point that it can raise the voltage, the battery is back to being a load.

I'll sum up what I've been trying to say all along because I think I got everyone worked up by saying a second battery does more harm than good.

My point is that if you have a GOOD battery under the hood, adding a second battery won't make an audible difference in the voltage EXCEPT under a current demand that's unlikely in a daily driver system. (My example was a 200-amp demand beyond the alternator's capacity. That translates to a amplifier power output of, very roughly, maybe 1200 watts ABOVE what the alternator can deal with continuously; if you think that's unrealistic in a daily driver system, say so).

So if you combine: a) a system with two batteries will put more load on the alternator than a system with one battery; and b) the improvement will typically be inaudible; then you can conclude that adding a second battery to most systems will do more harm than good, especially if you consider extra weight, extra cost, and extra install work "harm".

i used to think that way ........ only cost me a top 5 spot at world finals back when they were alot of competitors and large crowds that attended....//content.invisioncic.com/y282845/emoticons/blackeye.gif.66a1670f5aaf7f406e783a63e3387dc5.gif

If adding a second battery worked well for you in a competition system, then that's great; you have my sincere congratulations. But that doesn't necessarily translate to a good idea for most people in a system that's just for listening.

 

[audiolife 5,000+ posts]

yawnnnn!!!!!! ok for arguments sake we will are going to pretend there are no limitations on how much work 1 battery can do and that all daily vehicles can fit any size battery. also we will assume all batteries take just as long and are just as hard to charge as the next. lets also pretend that people dont need 250 or 300 amp alts because there is no one uses 1500 watt and over amps or even more than one, at the same time lets also assume that rpm doesnt play a role in output as at idle that alt must be easy to turn and real close to full output. heck ya! for a contest car they should do a car with like 7 alts and no more than 7 batteries lord knows that must win as it must put out at least 1.5 more volts than the battery. its not like the chain or belt would break that drives them or it would stall the engine...heck each alt only has 1 battery....them there vehicles with 1 or 2 alts and 50+ batteries never win nuffin! (note this post is supposed to look stupid)

in a propper system set up an extra battery wont draw more than 20 amps ever (20*14.4=288 watts) nothing in an audio system stays constant while playing meaning it will be under peak power most of the time so if your alt is working and of decent size its going to keep the battery probbably charged somewhat better than that. if you break it down i think its rather obvious a charged battery by itself

can put out alot more than 288 watts. after all to start a car takes between 400 to 600 amps to turn it over (that's over 4000 watts)........

 

[aaronmiiller 10+ year member]

Aaron im just going to tell you straight up dude, i wouldnt listen to anything these genius's say (no offense) i would just get a second battery for the back, and it will keep your amp happy, point made.

 

[Chevyaudio 5,000+ posts]

Get Dekas...good batts, and cheap. Please dont run an a Non Sealed battery in your trunk...bad Idea.

 

[audiolife 5,000+ posts]

Aaron im just going to tell you straight up dude, i wouldnt listen to anything these genius's say (no offense) i would just get a second battery for the back, and it will keep your amp happy, point made.

very basically in a real world app where you have sufficent power to cover the average draw of a system a battery will help. as it will help cover what the alt cant do due to rpm. some will say turn up the rpm, get a smaller pully or second alt. only problem with doing that is everyone of those things robs horsepower and gas milage and increases the wear and tear. people will argue back and forth...when you design your set up its pick your poison. imo mix them and get the benifit of using them both

 

[aaronmiiller 10+ year member]

X2^^^^ Get a second battery!!!!

 

[SSon22s 10+ year member]

I am wondering what I should do also, My car is a 2004 Impala with 2 Type Rs and a Viper D1200.1 my lights dim VERY bad at night and I want to make sure that the amp is getting enough current and there is less strain on everything else, I have already dont the BIG 3 and also have 00G running back to the amp, I am wondering if I should, 1) Upgrad the stock battery to a DEKA or Optima, 2) Add an optima in the trunk and get a cheap everstart or something under the hood 3) Get an Optima under the hood and have the alternator rewound, I am planning on getting and Optima since I get them cheap, and I also plan on changing from the Viper to a Sundown 1500 in a few months....