# How many watts can an OEM battery handle?



## skulboep (Nov 29, 2009)

How powerful of an amplifier or combination of amplifiers can a stock OEM battery drive before showing signs of voltage drop (i.e. lights dimming, headlights flashing, etc.)???

I know that a thorough and detailed scientific explanation probably determines this, but I am looking for a very rough layman's guide to this question. For those of you who are curious and want to offer more specific guidance, here is my particular situation:

I just bought a used 2002 Nissan Pathfinder. The dealer was nice enough to drop a brand new battery in the car, although it is an OEM replacement battery and is virtually identical to the stock battery it replaced (albeit it's brand new). I installed an Alpine PDX 4.100 amplifier (4x100W RMS) to drive 4 speakers (Polk MMC6500 components in front and Polk MM651 coaxials in rear). So far I have no problems. I want to add a sub. My options are to go with either a single sub or two. Depending on what I choose, I will need an amplifier that puts out between 500x1W to 1200x1W. I do not want to change my existing alternator, battery, add a capacitor or upgrade to the "Big 3." Long story short, I want to keep my existing electrical system in tact. What is the highest wattage mono amplifier that I can add to my existing system (already drawing 4x100W RMS) without having any manifestations of voltage drop? This will ultimately determine what sub setup I go with. Thank you for your thoughts!

Erik


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## freemind (Sep 11, 2008)

Well that Alpine is a Class D amp and if you get a class D sub amp, you will not be putting a bunch of drain on your electrical system IMO.

Make sure that you use 0 ga to ground your battery to the front in stead of the stock wire. Use the same size(0 ga)to ground the amps(ground both amps to the same point in back) and, 0 ga power wire from the battery to the amps.

You should be fine at that point.


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## Capt Steve (Dec 18, 2009)

It really isn't the battery that becomes the problem, but rather the alternator.
A battery is rated in AH (Amp hours). It will put out 12-12.5 volts for x hours depending on load. However, the alternator is what really supplies the power when you are running. 

If you have a 65 amp alternator, this mean it will only put out a max of 65 amps at around 13.5 - 14 volts. The formula to convert Watts to amps is watts/volts=amps.

So if your amps are pulling 600watt at 13.5 volts, you need an alternator that will supply 44 amps. 

Don't forget, that the alternator is also supplying everything else to the car as well. So if your lights are pulling 15 watts, and your coil is pulling 200 watts, and your amps are pulling 600 watts, now you need a minimum of 60.3 amps.

As mentioned above, you also need to make sure this power is getting to everything without any additional resistance. That is what the Big 3 does.

I don't think you need 0 gauge to the amps though. 4 gauge would be enough.


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## blazeplacid (May 19, 2008)

its not how many watts 

its how much current for how long


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## Oliver (Jun 25, 2007)

Capt Steve said:


> A battery is rated in AH (Amp hours).





blazeplacid said:


> its not how many watts
> 
> its how much current for how long


... or what captain steve said ^^^^^

current = amperes and hours = how long


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## t3sn4f2 (Jan 3, 2007)

1.21 Jigawatts! :wacko:


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## IBcivic (Jan 6, 2009)

t3sn4f2 said:


> 1.21 Jigawatts! :wacko:


FIXED...


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## HertzGuy (Jan 23, 2010)

1.21 JiggaWatts, what was I thinking?


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## teldzc1 (Oct 9, 2009)

So how would something like an optima battery help your system?


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## Capt Steve (Dec 18, 2009)

The point of my post was that no matter how big a battery you have, if your alternator is not up to the task it doesn't matter. If you take out more amps from the battery then your alternator can put back, you will drain your battery. 

Your alternator should be large enough to run your whole car, including your sound system, with the battery removed. Ideally, you only use the battery to start the car, after that, your alternator runs everything. The battery will just level out the voltage across the rpm range of the alternator output. 

And yes, a 1.21 jiggawatt or better yet, a 1.21 jigga amp alternator would be acceptable.


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## freemind (Sep 11, 2008)

One thing that all of are missing is, if he will be listening to his system while the vehicle is running or with it off.


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## skulboep (Nov 29, 2009)

Thanks for the input guys...I believe the stock alternator in the 2002 Pathfinder is 110 amps. And no, I don't plan on running the system with the car turned off.


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## Pillow (Nov 14, 2009)

Also depends at what volume levels you listen to your music. Loud will pull more current.


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## MIND_SOUL (Feb 12, 2010)

So doing the big three in MOST cases eliminates the need for an ALT upgrade or an additional battery?


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## YouSirName (Feb 1, 2010)

I'm running an Elemental Designs Nine.2x and a U.S Amps ClassDE1000 and haven't had any electrical issues on my stock alternator (which is only 90 amps) and stock battery. Although I don't really play it loud. I think you should look into getting a big subwoofer (15" or 18") and putting it in a big vented box that way you wont need a big amplifier to get some decent SPL. Also you should probably look more into the efficiency of the system as a whole instead of just one piece of the puzzle. If you can go with the 0 gauge if you plan on upgrading later on down the road. 0 gauge will also have less resistance than 4 gauge which means you wont have much of a voltage drop overall increasing the efficiency of your system. As far as amplifiers go, pick up a class D for sure with a high efficiency rate like 85% or higher if possible. Hope this helps.


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