2 batteries vs 1? (aka cold beer for cheap)

[monkeyodeath]

I've been doing a bunch of research on how to set up a basic system on my truck (03 Tacoma) that will allow me to run a fridge and some LED lights during desert trips where I might be parked for 2-3 days.

Let's say I want to do something simple and cheap (sorry if this is boring!). Should I:

a) Upgrade the starter battery in my Tacoma to a Group 31.
b) Add a second starter battery and an isolator.
c) Keep the 24F starter battery see how that works.

Either way, I'll be using a 200+ watt solar panel to charge stuff during the day. The vast majority of the trips I'll be using this setup for will be in treeless, godforsaken desert.

I realize, absolutely, that this is a bit of a half-ass poverty setup and that none of the above area totally ideal, but my needs are basic and I'd rather save money for gas right now. Just trying to keep it realistic and practical. If I find that my battery is trashed in 12 months, I'll take that as a lesson that I need more capacity. (Costco's got a decent warranty, anyway).

Plus, I've seen a few other forum members having success with solar and a single battery for running a fridge, so I don't think it's a totally bonkers idea.

I figure that my fridge will have a voltage cutoff and that's the only thing I'll be running much at night, so I don't need to worry about additional battery protection.

I considered getting a _true_ deep cycle as a second battery, but my alternator output never gets above 14.1V, so from what I understand I'd need to spend another $200+ on a DC-DC charger to be able to charge the battery on the road. (unless I rely on solar for all my charging) Plus, less-expensive deep cycles come in awkward shapes/sizes.

I also considered golf cart batteries, but in addition to the previous issue, they weigh something like 70lbs a piece, and I'd have to either fab up a majorly reinforced underhood battery mount, or put them in the truck bed and deal with the additional wiring/circuit breakers and lost space.

So, unless I'm missing something, the aforementioned 3 options are probably my cheapest and most straightforward way of getting some cold beer. Does a dual-battery system have some additional issues I'm not considering (aside from the extra cost of an isolator)?

 

[luthj]

It depends on your usage, but a 200W solar panel in sunny weather will handle most small fridges. In my opinion you will get much better performance with a dedicated battery, ideally in your bed. You can use a removable box to allow for easy removal when not needed. A pair of golf cart batteries are great for regular usage, but as you say, they are heavy (part of why they are so reliable). If you only plan on doing the 2-3 day cycle down a few times a year, then a decent quality dual-purpose flooded lead battery in the 100AH range will likely do the trick. Alternator charging is useful, but with decent solar, it won't provide much value for camping where you are parked a lot. If you have higher power needs than just a fridge/lights, then you can consider an alternator charge circuit. Most Toyotas don't see much over 13.9V at hot idle, so the charge rates for a direct line, especially with a bit of wiring drop, are pretty low anyways.

 

[john61ct]

For me, risking a flat Starter is not acceptable.

There are tools to ensure against that, but then maybe warm beer.

The LVC in your fridge is there to protect the fridge, set too low and not adjustable.

At least get an adjustable LVC.

Two identical G-31 designed for deep cycling like Odyssey 2150, one is House on the fridge side, then the adjustable LVC between House and Starter.

They work together as one bank as long as SoC is high.

But if it drops, Starter is isolated.

Occasionally swap so they wear evenly.

 

[DaveInDenver]

I ran a single group 27 battery for years in the old truck. It can be done successfully if you're conscious of watching the charge. I am lucky enough to live in a place where camping usually means deserts and mountains, which means cool overnight ambient temperatures even in the middle of summer. When I can I got in the habit of turning the fridge off at night. So I could usually go a weekend without worrying and never completely flatted the battery.

I did run it pretty low a couple of times that it cranked slowly, though. So in the new truck I decided instead of trying to squeeze a group 31 in I would run back-to-back dual batteries. In this case they each had to be smaller, a group 25 and group 35 take up about the same space as a group 31 and I got them where the group 27 once fit.

I went to Odysseys with group 25/35, each of which has slightly better specification than a single group 27 OEM Toyota True Start. So I did not lose any stock capacity in terms of starting CCA and reserve capacity. I was then able to offload the fridge completely to its own battery, which is rated 65 A-hr at the 20-hour rate. It's less than I would have gotten with a group 27 or group 31. An Odyssey group 31 is rated 92 A-hr @ 20-hour rate so I gave up about a day of running. But it's only going from 2 to 3 days, not really like I can go a week and so I run solar.

No matter how you break it down you need to run the engine or use solar eventually. Having dual batteries over a group 31 to me is just peace of mind for redundancy. I don't think unless you go with a truly large and dedicated bank do you really gain much for run time.

Of your options I'd suggest sticking with a stock size battery and adding a fridge battery. There has been a downside to my set-up, mainly the weight of 100 lbs of batteries in the stock location is beginning to fatigue the fender at the stock location. This would have occurred eventually even with a stock battery and going to a group 31 wouldn't have been any different. So moving weight to the bed or under the frame would certainly be a better option. But it's a compromise no matter what when you're dealing with a small truck.

 

[john61ct]

Not cheap, but LFP delivers Ah storage in half the weight & space.

 

[DaveInDenver]

Not cheap, but LFP delivers Ah storage in half the weight & space.

Significant cost and he's mentioned already having solar. If it was me I'd save the beer money.

 

[john61ct]

Yes, I was not suggesting for OP

 

[DaveInDenver]

Yes, I was not suggesting for OP

As a stock replacement?

 

[john61ct]

Just FYI in general

 

[DaveInDenver]

Yes, I was not suggesting for OP

Just FYI in general

For the OP I'd actually think an LFP fridge battery would make sense. It's what I would do now instead.

Don't bother changing anything in the stock system, keep a stock group 27 for starting, running the truck, winching. Then put a fridge-only battery in the bed or fit it somewhere under the hood.

The reason I did the back-to-back smaller batteries is due to not having much room to fit another lead acid battery of any size under the hood or wanting to take up much space in the bed. But lithium solves a lot of those issues and a smaller LFP wouldn't hurt the budget any worse than a Odyssey did.

 

[john61ct]

IMO "cold beer for cheap" makes a detailed discussion on LFP, OT for this thread.

 

[DaveInDenver]

That is the compromise. There's nothing as expensive as trying to do something cheap. The cheapest thing to do is buy the lowest end Walmart car battery, pre-charge it at home and run it from the existing solar in camp.

 

[john61ct]

Yes, saving money up front like that means a higher annual cost.

A good bank can last well over a decade if cared for properly.

Or get murdered in a few dozen cycles.

 

[monkeyodeath]

Thanks for all the input.

Guess maybe I should reconsider an external box. Would open up my battery choices. Since I'll only be using the house battery for the fridge -- and since the fridge will only be in my truck bed when I'm taking a trip -- I guess it makes sense to only haul a battery around if I'm actually using it.

 

[monkeyodeath]

For the OP I'd actually think an LFP fridge battery would make sense. It's what I would do now instead.

Don't bother changing anything in the stock system, keep a stock group 27 for starting, running the truck, winching. Then put a fridge-only battery in the bed or fit it somewhere under the hood.

The reason I did the back-to-back smaller batteries is due to not having much room to fit another lead acid battery of any size under the hood or wanting to take up much space in the bed. But lithium solves a lot of those issues and a smaller LFP wouldn't hurt the budget any worse than a Odyssey did.

Any examples of the kind of smaller LFP battery you're taking about?