Huge battery vs two medium sized ones

[G35Vortec454]

My recommendation

My recommendation for you.

Keep your starting battery and get a true deep cycle second battery, 100-200AH, 50-80W solar panel and a Sunsaver-duo controller. No isolator needed.The controller costs more but it features a built-in isolator for two batteries and will let your starting battery live a lot longer and can be used for more robust use later.

I've been using on-board DC power systems for 8 years and currently have a setup consisting a 660AH battery bank, 450W panels, 3000W inverter, 220A alternator, and 4000W Onan generator.

 

[Tony LEE]

I guess you can rationalise having only one battery by arguing that you only have one starter motor or fuel pump or whatever so one battery is OK.
However all the other components are single use and just sit there until they are needed. They were working OK when you arrived so no good reason to assume they won't work when you want to move again but the battery is dual use and can easily be made unserviceable due to simple forgetfulness.
Having a dedicated start battery is just good sense, especially if you intend going more than a few miles off well-travelled roads.

 

[Jack5885]

That wasn't how I was rationalizing it,

Here is why I'm leaning towards the single battery setup...

-Initial Cost and availability: As far as I know, there is no other battery with the same footprint as a PC1200. So to get a new battery I would probably have to order one online or find somebody nearby with one or two in stock. If I'm on a trip--even in the US--that isn't very convenient. Also, since Odyssey is the only company that makes a battery the size of a PC1200, I would have to pay premium for that battery. Replacing a PC2150 during a trip would be much easier since Group 31 batteries are stocked pretty much everywhere, and they would be cheaper since DieHard makes the same one for less and I also have the option of going for a Deka or Northstar battery of the same size. While the PC2150 is twice the cost of a single battery out of the dual battery setup ($400 vs $200), you don't have to buy an isolater kit which significantly increases costs. Single Battery wins here.
-Long term value: I separated initial cost and long term value because they are very different figures. I said this earlier but: if I understand how battery life works (and please correct me if I'm wrong), I believe I would have to replace the batteries on a dual battery setup more often, because I would be running the AUX battery through deeper discharge cycles. A full discharge of a PC1200 would be less than half of a discharge of a PC2150. Assuming that I use the same amount of power with either system, the AUX battery would age much more quickly. I believe that a single battery wins here.
-Simplicity of Design: With dual batteries, there is much more that can go wrong electrically, from more ground wires to faulty isolators to having the batteries fight each other (without isolator). For some problems there are simple and easy solutions, for others there are not. A single battery is pretty much a straight swap and so it wins here as well.
-CCA: With a starter and deep cycle battery, you only start your truck with the starter (unless you need a jump, but more on that in a sec). The PC1200 has a fairly average 530 CCA. Its more than plenty to start my car, but nothing special. The PC2150 has 1150 CCA or more than double the starting battery out of a dual battery setup. Single battery wins here
-Reserve capacity and Amp Hours: With the truck off and the dual batteries isolated, I will only have 78 minutes of reserve capacity and 44 amp hours. With a group 31 battery, I would have 205 minutes of reserve and 100 amp hours. This, once again, is more than twice the combined dual batteries. Single battery wins here.
-Backup: Here is where the dual batteries takes back some lost ground. If the starting battery fails, you always have the AUX battery to start the car. I agree that backups and failsafes are one of the most important things in a vehicle. If a dual battery dies, you have no way to start the car which would really suck, especially if the road that you are on is rarely traveled. Dual-battery setup wins here.


I originally asked which would be better because I think that having a backup in the middle of nowhere is extremely valuable. I thought that even though the single battery wins in most circumstances, the ability of not being stuck in the middle of nowhere was worth it. Then McZippie's post got me thinking about portable battery packs and generators. Would the money saved from a single battery setup be enough to cover the cost of a portable backup? Here is my cost breakdown to figure it out...

Dual Battery setup:
-$218 Odyssey PC1200
-$218 Odyssey PC1200
-$395 National Luna Split charging kit (This seems like a better and more reliable kit than the Kodiak Industries one)
-$??? battery tray built for Xterra (probably the kodiak industries one if I can get just the tray and mounting hardware). The price doesn't matter because it would be the same tray for the single battery setup (Group 31 is slightly smaller than two PC1200s).
--------------------------------------------------
Total: 830 + tray

Single Battery setup:
-$251.99 DieHard Platinum Marine Battery from Sears (Same as Odyssey PC2150 but MUCH cheaper) (woah!, when writing everything above I didn't realize how much cheaper the DieHard was.
-$??? battery tray built for Xterra (same as in dual battery setup)
--------------------------------------------------
Total: $252 + tray

Please point out if I forgot something because I don't want to unfairly judge these two options, but...
Total savings of Single battery over dual battery: over $500!!!

With that money I can buy:

$100 - A good quality 3-stage smart battery charger
$200 - Small generator (not a fancy honda or yamaha) but a reliable small 1000w portable generator
$100 - Two jerrycans for fuel

With that setup, I have the best of everything. I would have the best specs and be able to charge my battery if I do ever run it dead (which I doubt I would since I normally travel to a new campsite everyday). The generator would also provide power for anything that I didn't want to drain the batteries on. I would also use the battery charger if I had power at a campground to keep the batteries topped off even with electronics running. The jerrycans would mainly be for extra fuel for my car, but they would double as fuel cans for the generator. It wouldn't be an instant jumpstart, but it would work well and have other advantages (listed above)

I know many people swear by their dual battery systems, but if I can get much more for quite a bit less with great versatility and the only compromise being no instant jump start then I really can't justify a dual battery setup.

Let me know what you guys think, and please point out anything that I said that is incorrect. I'm trying to be unbiased in my analysis.


EDIT:
I didn't mention solar power because I'm planning on buying a RTT. Once thats installed, there is no more room for rigid panels on the roof.

 

[G35Vortec454]

If you decide on a generator for backup, especially a cheap one, make sure it starts when you need it. You could end up rebuilding a caburetor at the side of the road/trail. Generators need to be "exercised" frequently in order to be reliable. 20 to 30 mins twice a month or so should be enough. But that means fuel cost and your time.

And I want to reiterate the importance of true deep cycle; with your battery of choice it could become very expensive to be prematurely replacing batteries and although they have warranties, battery companies allow you to only exchange them enough times, unless you get them from Costco. Your starting battery could survive only a few deep discharges, after that it won't be able to crank your engine no matter what the CCA rating or voltage reading s.

 

[Jack5885]

I would NOT be getting a starting battery. It would be a hybrid/marine battery. Something designed to deep cycle but also put out enough CCA (Like the Odysseys). I would get a true deep cycle if I knew it had enough CCA, but since they don't rate true deep cycles that way, I don't want to take the risk.

 

[McZippie]

I would NOT be getting a starting battery. It would be a hybrid/marine battery. Something designed to deep cycle but also put out enough CCA (Like the Odysseys). I would get a true deep cycle if I knew it had enough CCA, but since they don't rate true deep cycles that way, I don't want to take the risk.

FWIW... For more reasons to have a single battery set-up research:

The advantages of deep cycling and fast charging of AGM batteries compared to wet batteries.
How the Peukert's Law effect battery size.
Automatic low voltage cutoff switches.

 

[bobDog]

Do you go out solo? Do you camp in austere locations? You have high draw accessories like fridge and inverter, how long do you stay camped at a site?

Single battery set ups are most common and obviously work well. One disadvantage they have over a dual battery set up is that a single battery is a single point of failure. Redundency of a dual battery set up should be given greater consideration if you travel solo or away from passers by who can jump start you or if you camp at a single site for multiple days. If you travel in a group or travel and camp in places that see traffic (potential assistance), a single battery set up's simplicity gets the nod.

Absolutely ...... 1 bat = total failure. 3 bat = 3 chances, duh...easy choice for me! Nothing like a cross cell short to ruin your day.....long walk if you're out of cell tower range.

Sent from my LS670 using Tapatalk 2

 

[G35Vortec454]

Don't we all wish we get 100AH from a 100AH-rated battery, or 40AH from a 40AH-rated one? It's very difficult to accept otherwise. Been there done that. Let us know how it worked out for you after a year, if your single battery ever lasts that long.

 

[MakersTeleMark]

Nice rationalization/analysis on the single battery equation, but I'm telling you, it's not the longest lasting, cheaper, or reliable way to go.

I've got 2 big *** starting batteries (1000 cca) under the hood (and 2 100 amp alternators), and a big boy deep cycle in the back. I can connect them any way I choose, or combine them. I can back feed my solar to the truck or the gens to the camper.

Having one battery and depending solely on that is like marrying your truck. You better trust that decision with your life.

Do you carry a spare tire?

 

[Jack5885]

Why wouldn't it last as long? People keep saying that, but I have not heard the reason why.
Also, Why isn't it cheaper? Am I not accounting for something?

Is a single big battery any less reliable than a single smaller battery?

 

[4x4junkie]

Internal shorts in a battery are quite rare (usually happens with neglecting to do proper maintenance on a non-maintenance-free battery and the water levels get too low, exposing the plates).

You are also absolutely correct, a smaller battery drained to 80% depth of discharge will last far fewer cycles than a larger one drained to 40% each time.

Like I mentioned already, having an auxiliary source of power available should alleviate much of the concern over getting stranded in the unlikely event your main battery became so discharged it can't start the engine. Thirty minutes on a 60-80 watt solar panel or a generator with a 12V out on it should easily be able to get you going again.

FWIW, my solar setup consists of two panels I attached to each other with a length of continuous-hinge on one side and a handle on the other so it can be folded up and stowed inside or cinched down on the roof or put anywhere there is room. It's portability also allows following the sun as it moves for maximum energy harvest. I just clip the controller's leads to the battery, set the panel out, and plug the panel into the controller.

 

[G35Vortec454]

Why wouldn't it last as long? People keep saying that, but I have not heard the reason why.
Also, Why isn't it cheaper? Am I not accounting for something??

We're trying to tell you the reason: experience - that's what you're not accounting for. Youre only considering what the batteries are rated at. You won't be operating with those batteries at 25C all the time, with perfectly clean cables and junctions all the time, with the perfect water level all the time, with proper charging and discharging, with the batteries sitting still all the time (ie no vibrations)' and many others. Do you prefer only one battery against these odds?

 

[bobDog]

...and when your Rig doesn't start you'll be stranded, get hungry and eat the rotten food and become sick and die.

Don't eat rotten food and die, bring one of these along:

http://www.alten-dc.com/gasoline-po...-volt-55-amp-gas-powered-battery-charger.html

This great!

Sent from my LS670 using Tapatalk 2

 

[Jack5885]

We're trying to tell you the reason: experience - that's what you're not accounting for. Youre only considering what the batteries are rated at. You won't be operating with those batteries at 25C all the time, with perfectly clean cables and junctions all the time, with the perfect water level all the time, with proper charging and discharging, with the batteries sitting still all the time (ie no vibrations)' and many others. Do you prefer only one battery against these odds?

How often do batteries fail like this? Is there a durability difference between bigger and smaller batteries? And if they do fail, can you still run the car with a jumpstart?

There is just so much to learn...

 

[G35Vortec454]

How often do batteries fail like this? Is there a durability difference between bigger and smaller batteries? And if they do fail, can you still run the car with a jumpstart?

There is just so much to learn...

How often? All the time, they are normal-use situations. The difference is just how severe the abnormality is at a given time and whether it's recoverable or not. My batteries right now are only giving out a quarter of it's normal output while I run the rooftop AC. And I'm 400 miles from home. One of the cables decided to overheat at one junction. Hence, one battery is over-discharging and under-charging, and thentwo other batteries are both undercharging and not able to provide enough juice because of that junction. That junction is supposed to pass 200A normally. My bzttery bank capacity is 660AH with 4/0 cabling throughout. And btw, my starting battery is an isolated Group 31.

To answer your question, a bigger battery or battery bank would tolerate normal-use conditions better than A snall one.