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Old 09-15-2014, 09:12 PM
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Adding an auxillary battery?

Anyone know anything about adding an auxillary battery to a car. I want to add an extra battery to my car for the lights? Pros and cons of doing this please. Also, should it be another 12v battery? How would it be installed if possible?

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Old 09-15-2014, 09:54 PM
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Unless you're planning on running the lights with the engine off for extended periods of time, an additional battery is going to do you a lot less good than just a larger alternator will.

If you do actually need an auxiliary battery, the way I would handle it would be to pick up a 12V deep cell with the most amp-hour capacity you can afford. I've had great luck with Odyssey Group 31s, but they are pricey and unbelievably heavy. You will need to isolate this battery from the rest of the electrical system at least when the car is shut down, so that using the aux battery's capacity doesn't drain down your starter battery. This can be as simple as a mechanical battery switch or something considerably more sophisticated and automatic. If you want to go a more hands-off route, have a look on Expedition Portal at some of the systems people are using on there to isolate their camper battery banks from their starting batteries. There are some very sophisticated and very clever solutions people have come up with.

If you are planning on running this aux battery hard, you still may want to consider a higher capacity alternator, since it's going to be working hard charging up both your aux battery and your starting battery, as well as providing for the considerable electrical load that the car wants whenever the car is running. Big electrical systems are hard work on small stock alternators.
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Old 09-15-2014, 10:14 PM
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Thanks for the info. I actually already swapped out my stock 80 amp for a 120 amp alternator with heavy gauge wires. I'm running 2 sets of hid bulbs and 2 sets of halogen bulbs plus 2 cameras and manual high/low speed fans. The alternator does a excellent job at handling all this, but if I use my remote start to turn on the car with the a/c and low/high speed fans on the car will not start unless I turn off the a/c and/or fans.
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Old 09-15-2014, 11:14 PM
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Before you go adding a lot of complication to your electrical system, consider whether a battery with additional amp hours and/or CCA will serve your needs. It does seem odd to me that the addition of a couple aux fans and the blower fan onto the starting load would cause a no start condition. For comparison's sake, a stock size battery in my W124 has no trouble starting the car, even with the A/C running, 1500W of stereo turned on, and the air compressor for my air ride running. And that's on a diesel, which already has the very heavy draw from the glow plugs. I'd be wondering whether your existing battery is up to snuff.
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Old 09-15-2014, 11:57 PM
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I was thinking the same thing, but the battery is just over a year old, 14 months to be exact. Do you think my festoon bulbs could be a problem? The license plate bulbs, glove box bulbs, and interior lights are the ones shaped like bullets. I got a good deal on some, but didn't realize that they were 24v instead of 12v. this is a recent change. Any issue with running the 24v bulbs in a 12 v system?
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Old 09-16-2014, 12:28 AM
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I can't imagine those bulbs are causing the problem, since those circuits aren't on when the car is started, leastwise if you're not leaving your lights on and your wiring isn't fouled up. I'd still want to change them out since they're liable to be half as bright running on 12V as they ought to be.

What brand battery is under the hood, and what voltage is it sitting at at rest? You should not be having starting problems with the small amp load you've added to the system, especially on a gasser.
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Old 09-16-2014, 01:36 AM
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12.6 car off. 14.4 at idle.
I think I figured out the problem, I've been having a high idle problem with my car and also very poor acceleration, I disconnected the IACV to lower the idle whcih brought it down to about 12rpm, but at the start up its really rough before it smooths out. I think that the really rough initial start causes he cr not to start when I have the accessories on and I use the remote start. Of course all of this is just a theory until I go test it out, but I think that may be it.

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