Recomendations: How to set up an extra battery for my system

[fluxwildlyuncut]

I was thinkin of addin an extra battery in the boot of my car to run my system off and was wondering what is the best way to do it and if anyone had any recommendations or advice on the best ways to to it.

[kopper69]

This is a common practice for 4wd's etc who want to run accessories but dont want to discharge their main battery. Just before I give any advice though, have you considered upgrading your battery? Adding a second is a bit of an investment, few hundred dollars by the time you get the equipment, cable and the second battery. There is also the time running the cable through the car and the potential risks if the power cable was ever to get damaged and short out. You may be better off spending a bit more and getting a better battery?

Anyway if you are still set on the idea of a second battery, you will need to go and purchase a dual battery kit. If you want you can purchase a kit from jarcar and make one up from scratch. The kit basically consits of a switch which can be either manually controlled or automatically controlled. For your application, go for an automatically controlled. This switch will disconnect (or isolate is the word used) the main battery when the car is turned off and leave the second battery (or auxillary battery) to supply power to whatever needs it. In this case the audio gear. You can run the battery fairly low, to a point where it wouldnt normally start the car. But when you go to start the car, the switch (aka solenoid) will switch back to your main battery so that you can start the car without any problems.

The car will charge your main battery back to full and then, because it is automatic, it will charge the auxillary battery.

With a manual system, you need to do the bits that the automatic solenoid would, so you need to remember to switch a big switch each time you need to use the auxillary battery so you dont drain your main battery. Good if you dont use it often, but not good for your example.

Mounting the battery. Batteries cannot be enclosed. They need ventilation to remove the gases that are created when they are used. Just remember that when looking for a spot and make sure that the battery could not ever move once it is in.

If you want to research more look up 'dual battery kit' or something like that for a heap of information. When you make your mind up you can go to a 4wd or camping place and purchase one of these kits. Installation instructions will be included.

You do have the option of simply joining the second battery in parallel, but it is not recommended. This will give you a much bigger combined capacity, but both batteries will discharge to the same level, meaning you may not have enough juice to start the car. It also adds a huge demand on the alternator as it now has to charge twice as much as it normally would.

Good luck, let us know what you decide on.

[Tasmaniak]

Have you considered the use of a Bat-Cap?

[fluxwildlyuncut]

Cheers for the great feedback!! i already have a cable run for the battery (the one going to my amp presently), and was thinking of making a little box or compartment for the battery behind my sub (lucky i didn't though).

The only reason i wanted an extra battery is that i was worried about draining the battery listenin to music and then being stuck somewhere. I got caught out installing and adjusting everything and it only took about 15 mins for the battery to run flat.

However, how well does installing a capacitor on the power line work. If that will help out my battery and give me a little extra power, then i might go that way. What sizes dio you recommend?

[Tasmaniak]

Not a capacitor....but Bat-Cap. It looks like a motorcycle battery but it's capable of supplying around 800A for approx 30secs... Taken from a Bat Cap manf website

What is a BATCAP?

A conventional battery, as we all know has a positive and negative terminal. The chemical reaction within creates a flow of electrons, causing an electronic device (in this case an amplifier) to work. The stiffening capacitor is similar to a battery in that it stores a charge. The fundamental difference is it cannot create electrons. It can only store and supply (discharge) them upon demand. The advantage with a capacitor is that it discharges in one twenty thousandth of a second, unlike a battery that does in one second. The battery therefore cannot discharge fast enough to effectively supply the amplifier and this is the reason for "power sags."

WAKE UP! Don't fall asleep just yet, we're getting to the exciting part!

The XSTATIC BATCAP© is simply a battery that can discharge just a s quickly as a capacitor. Therefore, you have a constant supply of electrons that will discharge at lightning speed. This puts less strain on your stock alternator and battery. It also recharges faster than a conventional battery since the internal resistance is low. How about the install? Well I'm sure you can find a place to put this 2.5lb. baby and his 5lb. big brother. Don't let the size fool you though. These BATCAP's can crank your car, and you can bet we put that to the test!

The cost is another remarkable feature since the 300 model costs the same as a "High End" stiffening capacitor and the 400 model costs a little more. Remember, "good things come in small packages." (I was going to say that "SIZE" doesn't matter but, let's not offend anyone now.) Oh, by the way, the fact that the BATCAP© is capable of discharging in a RUSH over a 5-10 second period SCREAMS three letters, "SPL!"

Home of the Batcap

[kopper69]

. I dont think a bat-cap is what he needs by what he has mentioned. It sounds like its not much more than a cap. The site doesnt mention anything on capacity, but I would guess that this thing wouldnt provide power to the car for more than a minute once the car is off, giving up most of its juice on a few bass notes. Its advantage is that it can provide alot of power in a short time, I dont think its capacity is any advantage though - and what we want is power for a longer time, which is what a battery offers. Would still be recommending a dual battery setup.

[commsirac]

The only reason i wanted an extra battery is that i was worried about draining the battery listenin to music and then being stuck somewhere. I got caught out installing and adjusting everything and it only took about 15 mins for the battery to run flat.

Ok, what you perhaps really need is a timer or a battery voltage sensor that will shut down your stereo.

Im not aware of commercially available devices here.

One way which I couldnt atest to working perfectly all the time is to have a relay controlling power to the head unit and to put a resistor in the trigger lead to the relay which will cause the relay to trigger off once the batt falls below 12.4V or so, however, though this would be sensitive to voltage fluctuations caused by peaks in the music.

Perhaps explore the timer route.

[Tasmaniak]

. I dont think a bat-cap is what he needs by what he has mentioned. It sounds like its not much more than a cap. The site doesnt mention anything on capacity, but I would guess that this thing wouldnt provide power to the car for more than a minute once the car is off, giving up most of its juice on a few bass notes. Its advantage is that it can provide alot of power in a short time, I dont think its capacity is any advantage though - and what we want is power for a longer time, which is what a battery offers. Would still be recommending a dual battery setup.

heh, it helps if I read his first reply properly eh? Although a bat-cap is HUGELY advantageous over a capacitor it is definetly not what we want here.

This gentleman either needs a dual battery isolator set-up or a battery saver device. Which is common in newer vehicles. Anything left running after the car is shut off is automatically shut off after a set period of time or when the battery falls below a set point. There are plenty of devices out there for this which is probably recommend over the second battery route.

Koolatron 12V Battery Saver – Car Battery Saver – Automotive Accessory

A device such as this wired in through ACC on your headunit will work well...or even on the remote line of your amplifier. Just need to be wary that it doesn't shut off on heavy bass beats?

[commsirac]

Koolatron 12V Battery Saver – Car Battery Saver – Automotive Accessory

?

Yes, thats the sort of thing, but its described to shut off after the batt voltage hits 11V. My experience, anything less than 12.3V and there may not be enough in the battery for a start.

[Not_An_Abba_Fan]

Run the second battery but use a deep cycle. Have an automatic controller so that you don't have to worry about forgetting to switch it back all the time. As kopper said, it will automatically isolate the cars starting system when switched off so you are only running the accessories off the auxillary battery.

You can enclose a deep cycle to a point, but not fully. There are battery boxes available that are held in by a strap.

The only downside is room and weight.

[Tasmaniak]

It's rare that a car won't start at 12.3

[kopper69]

It's rare that a car won't start at 12.3

Not sure where this post is relating to, maybe a mistake? But it depends on the condition of the battery. A new battery at 12.3V probably would, an older battery could very easily fail to start the car if it was at 12.3V.

[commsirac]

It's rare that a car won't start at 12.3

As I said, in my experience, once below that voltage it can get dicey, especially when the temp gets lower and the battery gets older.
I dont know about your experience, but best not to second guess what I post.

Perhaps have a look at Car and Deep Cycle Battery Frequently Asked Questions (FAQ) Section 4 for open circuit battery voltage versus level of charge at various temps.

[garfa]

so what your trying to say is that there could be a difference of 0.06V if the batt is between almost 40 and 4 degrees C........
R...I...G...H...T.....
probably get a bigger voltage difference over dirty terminals.....
stop being a keyboard warrior and acting like you are the king of the hill.

[commsirac]

so what your trying to say is that there could be a difference of 0.06V if the batt is between almost 40 and 4 degrees C........
R...I...G...H...T.....
probably get a bigger voltage difference over dirty terminals.....
stop being a keyboard warrior and acting like you are the king of the hill.

What dont you wait for a reply before asserting yourself here, then you wont need to wipe the egg of your face.

You obviously havent taken in what I said. As the battery gets near the critical 12.3V level/50% charge level then it can be critical(not turn the starter over fast enough) with an older battery or at cold temperatures.
There is a table in that link that shows you how the voltage of battery underload drops with temperature....have a look.

[garfa]

reply from whom exactly, the bloody pope!
i have read the whole page, cannot find much there.
yes, temp does have an effect but less than .06 under normal australian conditions.
all that you have shown is that voltage of an LA batt is effected by temp, marginally. which we all knew.....
this does not address the issue that a batt w/ 12.3v will start a car 99/100.

[commsirac]

reply from whom exactly, the bloody pope!
i have read the whole page, cannot find much there.
yes, temp does have an effect but less than .06 under normal australian conditions.
all that you have shown is that voltage of an LA batt is effected by temp, marginally. which we all knew.....
this does not address the issue that a batt w/ 12.3v will start a car 99/100.

Oh dear, I only provided the link for people to verify hopefully what is generally known, and for the fact that at ~12.3V a battery is only half charged. As you can see(well maybe you cant) even when nearly discharged completely the voltage doesnt really fall below 11.8V, which makes the device that isolates an appliance 11V not really well designed, WHICH WAS THE MAJOR point under discussion that related to the thread....but some want to try and start brush fires and catch me out on details......not on this issue Im afraid.
Here is a summary of that info directly from the link:
For example, if the electrolyte is at 20° F (-6.7° C), the Open Circuit Voltage reading would be 12.696 for a 100% State-of-Charge. At 100° F (37.8° C), the Open Circuit Voltage reading would be 12.308 for 50% SoC and a reading of 11.773 or lower at 120° F (48.9° C) would indicate a discharged battery.

Most people know that a battery that is on the way out usually first struggles when its cold(how come you dont?), and its not because the open circuit voltage(Im guessing you dont know what that means) drops by 0.06V.... in simple terms, the chemical reaction in the battery doesnt go as well when it is cold.

Go back and look at the Capacity Load Test which shows battery voltage under load versus temperature, which shows how under load the difference in output is close to 1V with a 40C temp difference, that's with a battery in good condition with 80% charge. 1V difference at the starter can easily make a difference between getting the motor to spin fast enough to start.
It gives some indication of what lies in store with batteries with more travelled batteries at lower levels of charge where the voltage will drop more quickly in a start situation and further.

[Not_An_Abba_Fan]

Which is why I still recommend having a second battery to run accessories. The risk of having a battery drop below the critical starting voltage is all that you need when you are alone in a carpark thumping out some rad tunes.

[garfa]

Oh dear, I only provided the link for people to verify hopefully what is generally known, and for the fact that at ~12.3V a battery is only half charged. As you can see(well maybe you cant) even when nearly discharged completely the voltage doesnt really fall below 11.8V, which makes the device that isolates an appliance 11V not really well designed, WHICH WAS THE MAJOR point under discussion that related to the thread....but some want to try and start brush fires and catch me out on details......not on this issue Im afraid.
Here is a summary of that info directly from the link:
For example, if the electrolyte is at 20° F (-6.7° C), the Open Circuit Voltage reading would be 12.696 for a 100% State-of-Charge. At 100° F (37.8° C), the Open Circuit Voltage reading would be 12.308 for 50% SoC and a reading of 11.773 or lower at 120° F (48.9° C) would indicate a discharged battery.

Most people know that a battery that is on the way out usually first struggles when its cold(how come you dont?), and its not because the open circuit voltage(Im guessing you dont know what that means) drops by 0.06V.... in simple terms, the chemical reaction in the battery doesnt go as well when it is cold.

Go back and look at the Capacity Load Test which shows battery voltage under load versus temperature, which shows how under load the difference in output is close to 1V with a 40C temp difference, that's with a battery in good condition with 80% charge. 1V difference at the starter can easily make a difference between getting the motor to spin fast enough to start.
It gives some indication of what lies in store with batteries with more travelled batteries at lower levels of charge where the voltage will drop more quickly in a start situation and further.

No, what you brought up originally was that temp effect the batt.

Now read your chart, and you can clearly see that even if the battery went from almost -20 degrees to almost 50 degrees C the battery voltage will change LESS THAN 0.15 volts.

So a 12.3 battery will start a car regardless of temperature.

I have included your original statement below

A new battery at 12.3V probably would, an older battery could very easily fail to start the car if it was at 12.3V.

Anything to add?

[| evaN |]

i was running 2 deep cycle batteries with a redarc battery isolator and if you've got a decent system, the front battery wont be full enough for long enough for the isolator to which over to the rear battery to charge it. if you're going to upgrade the alternator then go duel batteries, otherwise don't bother.

[commsirac]

No, what you brought up originally was that temp effect the batt.?

It certainly does, both the open cell voltage and most importantly the voltage under load, starting ability.

Now read your chart, and you can clearly see that even if the battery went from almost -20 degrees to almost 50 degrees C the battery voltage will change LESS THAN 0.15 volts.?

Yes, that is open cell voltage. The only interest in open cell voltage and temperature is assessing the level of charge of the battery. An open cell voltage of 12.3V tells us the battery is half spent.

So a 12.3 battery will start a car regardless of temperature.?

No. If its a battery where 50% charge is still big compared to the starting demands of the car possibly. If its a battery on the way out 50% may not cut it, or if the temperature is low the voltage when cranking will be affected greatly too.
Its clear to me you have no idea on the terms open circuit voltage and closed circuit voltage under load. You are right the open circuit voltage varies only slightly with temperature, however, this is not the case with the voltage underload. Im only concerned with getting the car started!

I have included your original statement below

Well, actually its Kopper69's, however, it supports what Im saying, so Ill stand by it too!

Anything to add?

Please read all the information carefully.
If you really want to improve your understanding in this area, I am willing to help, however, you are not going about it the right way.

the bottom line is that the device that isolates the battery from the load at 11V is going to be useless if a battery is completely discharged at ~11.8V.
Ive given you a figure of 12.3V can be dicey. I didnt pull that out of fresh air, or even need to go to the link I found for you and others.
Its from the experience of dealing with keeping five cars on the road for the last 30 years in cold and warm conditions.

[VNV6VENGEANCE]

The only thing worthwhile to this thread is the suggestion to upgrade your alternator if you want to add a second battery. If you really want to talk **** about temperatures creating fluctuations in batt voltage go do it on a thread where it can supply help to someone that needs it. All he needs to know is how to get the job done.

Whats with all these keyboard warriors on here...? People come on here to learn about their rides not to listen to your crap. You guys must have better things to do...surely there are cannons lying around that you could install on your rides...?

[immortality]

All he needs to know is how to get the job done.

surely there are cannons lying around that you could install on your rides...?

thats becoming a major problem with this site. people ask a simple question and you get bombarded by people who say your wasting your time, it isn't worthwile and a whole lot of technical **** that isn't important

cannons on commodores....... fairly sure no members on this site would admit to that

[kopper69]

The only thing worthwhile to this thread is the suggestion to upgrade your alternator if you want to add a second battery. If you really want to talk **** about temperatures creating fluctuations in batt voltage go do it on a thread where it can supply help to someone that needs it. All he needs to know is how to get the job done.

Whats with all these keyboard warriors on here...? People come on here to learn about their rides not to listen to your crap. You guys must have better things to do...surely there are cannons lying around that you could install on your rides...?

If a dual battery switch setup is employed there is probably no need for the added expense of upgrading your alternator as the alternator is only ever charging one battery. If you put the two batteries in parallel, you would need to look at upgrading your battery, but as I said above, not a good option.

[Tasmaniak]

I am SOOOOOOO going to get flamed for this. Get two brand new batteries that are identical same brand, size, same CCA and all the other what nots and simply parallel those bitches together.

I feel the heat coming on already.

Just to add fuel to the fire and I'm not joining anysides... I had a similar discussion with a gentleman similar to this 4months ago. He told me my car would NOT under any circumstances start if the battery is below 12.5 well I know that this was a crock and he said to bear in mind that we are in Alaska and yadda yadda yadda....long story short.

I deliberatly left my interior light on in my car. Came out the next day and measured the voltage at the battery. 12.14 Figured that I was screwed and was definetly going to need the isolated battery to start this. Thought I would try anyway...Removed as much load from the battery as I could, turned the key cranked slowly for a split second and then fired up. Battery has a build date of 5 years ago so I can only presume it's been service for at least four years.....here in Alaska.

So status...
12.1 Volts
4 year old battery that has been in hard service
-30C
Vehicle started...after a hard crank.
3.0L V6 Engine 9.3 compression ratio
Oil Viscosity 5w20 (this plays a part as well, don't forget that!)

I have some more gasoline for the fire if you folks want? LOL

Bear in mind, this is ONE vehicle....