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Old 05-18-2011, 04:49 PM   #1 (permalink)
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Question What range do Deep Cycle Batteries give with out alternator?

Ok, so I know there are a lot of factors here. First of all I am driving a 94 VX with some mods and getting about 60mpg. My battery has been slow to crank and after further investigation it seems it's due for a new one . . . hmmm, deep cycle . . . no alternator. . . tempting
So I think I found a place I can pick up some decent used deep cycle batteries at a good price. Then I need a charger and a way to monitor voltage. But I am wondering what kind of range I can get with out an alternator. I drive 50 miles to work and 50 miles home. Usually won't need headlights, also considering led headlights. But I will need to run a/c a good bit as the summer heats up here in GA. I also have one 10 inch sub with a small amp, I can live with out if I must, but would rather use it at moderate volumes.
I am hoping that 2 decent sized batteries in the hatch will be enough. Maybe even one more small one to replace the original battery. What can I expect, and is it reasonable to still use stereo and sub?

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Old 05-18-2011, 05:18 PM   #2 (permalink)
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To really know for sure, I'd highly suggest measuring how much power your car uses during normal usage.

For my Paseo, I think its around 25A with the engine on. Using that as a basis, if your drive there is 1hr and home is 1hr, you're using 50Ah. This means you need a 100+ Ah battery to keep the depth of discharge under 50% and extend battery life. Most group 31 batteries are around 100Ah. However, if you want this to work in winter you need almost double that.

Here are some threads to read over:
Current project: A better alternator delete
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Old 05-18-2011, 10:27 PM   #3 (permalink)
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One of my friend did 200km on a swift gt with no alternator belt on a freshly charged battery (he was 200km away from home)...

Of course he had a spare one in the back.

He did that on a standart car battery so a deep cycle could go farther between charge.

Deep cycle battery can be bought under 100$ so I don't think it's a good idea to buy a used one.These won't fit also in your battery tray as the civic's one is really small.
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Old 05-19-2011, 03:06 PM   #4 (permalink)
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With how the P07 ECU handles the alternator, I'd be interested to see if there would be much of a gain by taking off the alternator belt.

I know that the ECU will "turn on" the alternator when the ELD sees more than a 10Amp draw on the system. This time of year in MN, it stays warm enough to not need the heat and cool enough to not need the A/C (my VX doesn't even have A/C anyways). So when I'm driving around with the windows cracked and the climate controls off and no headlights during daylight hours, my voltage gauge indicates that the alternator is not actively charging the battery most of the time. I forgot the specific RPMs but once you get over something in the 2400rpm range the alternator will be turned on as well. Most of the time during the summer even right after I start the car, the alternator will not be charging the car. But turn on the blower motor past the first setting and the alternator kicks on and starts charging.

Basically, I believe that the VX might benefit from your deep cycle battery idea, but maybe do some testing and a cost analysis first to see if it's really worth it. If it's going to take ten years or more to recoup the cost of the deep cycle, I'd just stick with a normal starting battery.

I've actually had a deep cycle AGM Optima in my VX....the way the VX charging system works actually ruined the battery causing me to switch back to a standard lead-acid starting battery.

So if you decide to go through with this be sure to document and test A-B-A and share the results with us, please.


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