Dual Battery Question

what about just upgradding your battery? I know Kinetic makes some really good batteries. Instead of spending the money on 2 batteries and a new alternator you could use the money for 1 battery. This way you save weight and dont have to worry about putting the other battery somewhere. Maybe you could get your factory alternator rebuilt to put out more amps or if the 4.0 alternator will fit look into the higher amp from the toying package.

 

I already did buy a new battery thats pretty beastly. The problem is when I start running all my audio stuff with the lighting, it'll drain it pretty hard. Plus, I go camping and could use the extra reserve capacity as well as when I use my sound system at the drive ins. For my system set-up now, the upgraded battery worked, but now I'll be adding more devices that are going to suck down the juice pretty hard. Thanks though! I did look into getting the factory alternator rebuilt, but I think i'd rather spend a few extra $$$ to get one that was made originally to do what i need it too.

 

You are correct, make sure the batteries are of the same CCA / Ah rating. I work with uniterruptable power supplies and we often parallel "batteries" together (we refer to a 40 12VDC block system as a 540VDC battery). It may shorten the life of the Alternator depending on the quality of the manufacturing materials but I expect it would last as long as the batteries do.

 

oh wow, excellent. I've contacted two companies about an alternator, mean green and extreme amperage. I told them what I'm planning on doing, so, hopefully the will have some insight as far as alternators go. Do you think I will have any problem without using an isolater? I dont really think I need one...and if i could spare the expense there, i'd rather put that money into a really high quality alternator

 

I would say the money is better spent on the alternator. The isolater is a good idea for a redundant system (to have a back up battery in event of failure in the primary battery) but if you require more capacity paralleling 2 batteries is the ticket. I would suggest you add up all of the current draw from your accessories when sizing the alterntor, batteries and the cable you may find that you do not need a larger alternator but as they say bigger is better.

 

You have a good point, but I'm a fan of over engineering. I'm not worried about not having a battery back-up because I use the prioritystart promax, but I am afraid of killing my stock alternator with running two very large batteries. I'm not sure what exactly the stock alternator is rated at, I think like maybe 80-90. I upgraded my stock battery to a marine battery, and will be getting an identical automotive battery to it, same specs, just 2 terminals instead of four. It's because of that I think I'd be better off getting a bigger alternator. Thank you very very much for all your input! It's appriciated!

 

Mixing deep cycle with conventional is not a good idea, unless you have an isolator. The deep cycle can tolerate being run down low, conventional will be junk after 3 deep cycles.
Keep the batteries identical if they're not isolated from each other.
There has to be a chart/formula for what size alt to use for two batts. I don't know.

 

Oh wow, very good point, after reading that, i jumped on sears webpage, I didnt realize that the P-1 wasn't a deep cycle...at least it didnt say it was. I'll just grab another PM-2. Thanks for pointing that out!!!

 

No prob. Wish I could help more with the capacity issue.

 

its ok, not a problem! I was too concerned with matching up the specs of the batter, cca and reserve capacity, I didnt even bother to check that the other battery wasnt a deep cycle.

 

A buddy of mine has a Jeep Grand Cherokee that we installed a dual battery system in.

He has a yellow top optima in the stock location, everything is connected to the optima. We then used battery cable to wire the second battery to the stock battery terminals and installed a constant duty solenoid in between. The second battery is just a standard battery from NAPA.

The theory was that it did not matter what drained the optima, lights, stereo, extended cranking. The second battery is held in reserve so he can always get it started. We wired the solenoid so that it is engaged only with the key in the on position (not start or Acc). In the event that optima will not start the jeep, there is a switch on the dash to manually engage the solenoid with the key in the start position. Basically, the jeep will jump start itself. After it's running, he just leaves the solenoid switch turned off to isolate the batteries. After the alternator has had a chance to charge to optima back up (the aftermarket voltmeter makes it possible to gauge this), he moves the switch back to the normal position.

The only problem with this is that the optima yellow top is not a true deep cycle. It is supposed to be capable of both starting and deep cycle duties. This does not seem to work in his case, he goes through optimas fairly quickly. He is considering moving the factory dome lights, headlights, and all his stereo and off road lights to an aux fuse panel, getting a blue top optima (true deep cycle) for it. Then we would move the standard battery into the stock location and never run the starting battery down.

Your mileage may vary, I know that the local ambulance company has all their batteries (four in each unit) connected by solenoids. They use four of the same battery, one pair runs the radios, etc with the truck off, the factory pair is isolated and always protected from running down. The only thing that will kill all the batteries and not allow a self-jump start is to leave the key on with the engine off. A battery isolator and seperate solenoid for the self jump would solve that. They don't have issues with the batteries dieing early, but they don't deliberatly run the batteries down.

 

Hmm good information. Thanks! My reasoning for the second battery isnt really for in case of killing the first...I wanted it for the capacity. The idea is, if I have 2 batteriest hooked in parallel, my voltage wont be dimminished as much as if I was only on one battery when running many electrical devices. I bought the promax to make sure I dont do something stupid and leave a light on and kill two batteries. Thank you for your input though! very helpful!

 

Maybe the first thing you should do is get your charging system checked out. Find out how much power you are pulling with everything on and how much the alternator is capable of putting out. Maybe you don't need to worry about running the battery down.

In the event that you are pulling more juice than your alternator will supply, upgrading the alternator would be best.

If you can't upgrade the alternator to keep up with demand, then two batteries makes sense at that point. If they are two identical batteries, then you don't really have to have a solenoid or isolator. A diesel truck will have two identical batteries in parallel. Nothing wrong with that, just figure that if one of them goes out, it is going to drain the other. Same result as stock, can't start your truck. But it sounds like that's not your main concern.

I would start by finding out what the stock system will do. Perhaps all you need is one high quality battery.

 

The stock alternator puts out 80-90 amps, i can't find for sure, but I've seen people post both those two numbers. I bought a high quality battery, which works for my system now, but I'm adding an amp, and either 3 hella lights and 2 whelen landing lights, or just 5 hella lights. I'm not entirely sure what the hellas will draw, but I know the whelen landing lights suck juice like candy. I imagine 5 hellas will draw a substantial amount of power. but I will definately look into it. Thanks very much!

 

Have you considered HID? Even if you do have all this great electrical hardware it won't hurt anything to have less draw.

 

Eventually, I'd love to have all of my lights HID. It would just be super expensive to do it all at the same time...at least I'm under the impression I would. I could be wrong though, wouldnt be the first time! I'll def look into it. I prefer the look of HID, and I'd love to have less draw. Think if I went all HID, that my stock alternator could get by powering/charging both batteries?

 

I'm sure it could "get by" but I don't know how long or how well. I wonder if you could run stock and monitor it somehow for a while. Do you have a scan gauge or the equivalent? If so you can run the batteries down a bit and see how long it takes to charge them back up and compare with some numbers that you get before.

 

I do have a scan guage, and good call, didnt even think about that. I suppose it can't hurt...worst case senerio...i kill my alternator, so I just go buy the one I was going to anyway. I'm thinking you have a really good point with the HIDs. If I go and get 5 hellas, instead of 3 and 2 whelens, and use the extra cash from not buying the whelens, I could probably outfit all 5 hellas with HIDs, and still have enough to put HIDs in my head lights. I really do like the look of HIDs...now i can't decide. My uncle is a pilot and his company gets heavily discounted parts, such as landing lights. He is the one who suggested I put on some Whelens. They are rated for 14v, I'm going to have him ask his techs what they think as far as running them off of my system and if it can handle it or not without a bigger alternator.

here's a link to the whelen lights (please note theres no way i'm paying the manufactures price for them)
http://www.aircraftspruce.com/catalog/elpages/ledLandingWhelen.php

I'm thinking maybe the HIDs are the best way to go

 

Yessss Identical batteries....

You may be fine if they have the exact same specs and are different brands but as you can see with the Peukert formula (Google it) not all brands put out the same juice in the same way. They may say the same specs but they are made differently and do NOT put out the power in the same way.

If you are going to parallel 2 batteries buy them brand new so that they are both at the same stage in their life otherwise one will draw down the other and cause you problems. Also get the same model and brand. this is very important. batteries of different makes and in different stages of there life can react to each other in a bad way as well. you must be careful.

 

I like the idea of the aircraft lights. It seems they would be designed to illuminate a whole runway which is obviously much wider than a street. That could be a very good thing. Also with them being LED they probably draw even less than hid.