Anyone use a small 12V marine battery as a house battery?

Greg said:
Well, my question wasn't really about dual battery systems. I think that's been pretty much covered. Perhaps the details I added were unnecessary so lets just skip them and go for the end results of the theoretical situation.

For whatever reason:
  • We have a situation that results in one battery hovering at 50% capacity in a dual battery system for extended periods of time.
  • Under the same conditions we a single battery system hovering at 75% capacity extended periods of time.
Build them however you want. In this head-to-head competition where both systems are placed under the exact same stress which system will crap out first.
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If you're comparing a 100AH 12v AGM vs 2x 50AH AGMs. The single AGM that's running at 50% capacity will likely crap out in under 2 years, they simply don't like sitting low for prolonged periods of time unless you're constantly cycling them which is a bit of a different story. Depending on luck on the plates during the manufacturing process it might do year 3 and 4, but usually sitting that low allows for some sulfur crystals to form and it's a cumulative effect over time.

With some of the larger capacity Odyssey AGMs, they charge better at 14.6v so having a DC-DC AGM charger helps here.

With a single Group 31 AGM, using a Schottky Diode or germanium diode in the Voltage Sensing Circuit of the charge system will bump the volts .15-.46 (or .2 if using germanium) which is enough to charge the Odyssey 31-PC2150s (12v 100ah AGM) at a standard rate. Silicon diodes drop the voltage too far (.6v) and could potentially cause some electrical issues for some folks.
 
As for me, I like separate batteries. One just for starting. One deep cycle for luxuries in camp.

This IS the safest route. Anything else is a risk.

YMMV.

:coffee
 
As I said numerous times. As long as you go the distance, AS MOST HERE HAVE DONE OR WOULD DO, to make sure you're charging that second battery TO FULL between uses, you're wasting your money.

My experience, however, is that most of the folks coming onto the "overlanding" scene with their first vehicles refuse to do so.

If your goal is to isolate your starter battery from auxiliary loads, then yes, mission accomplished.

But if you think that's the only problem you need to protect yourself from with regards to your charging/power storage solution, you're mistaken. A battery isolation solution is only a solution to maybe 10% of the problem.
 
  • Mitch said:
    As I said numerous times. As long as you go the distance, AS MOST HERE HAVE DONE OR WOULD DO, to make sure you're charging that second battery TO FULL between uses, you're wasting your money.
    Click to expand...
Mitch said:
My experience, however, is that most of the folks coming onto the "overlanding" scene with their first vehicles refuse to do so.

If your goal is to isolate your starter battery from auxiliary loads, then yes, mission accomplished.

But if you think that's the only problem you need to protect yourself from with regards to your charging/power storage solution, you're mistaken. A battery isolation solution is only a solution to maybe 10% of the problem.
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I'm just going to sum the expectations to hopefully end this bickering.

I'm assuming that 90% of the the problem being a combination of the following:

  • poor planning
  • false expectations
  • false sense of security from not properly understanding the system that is employed
A person who plans well (keeps their backup tested and fully charged), knows not to drain their battery beyond a safe margin (proper expectations), and uses proper battery monitoring tools (proper verification ie security) will be likely be fine.

Though, I still drive stick and park on the top of a hill, have ham, satcom, laser pointers, signal mirrors, extra, food, water, and other supplies just for the simple reason that if all else fails, I'm not SOL.
 
So does Andrew St Pierre White have it correct? He seemed to explain it well in laymen terms.

Side note, what is everyone's opinion on a system like the National Luna DIY split charge system?


 
Robert said:
So I was under the truck again scheming out a different mount for my air tank and I got to looking at all of the space between the bed and the quarter panels. There is plenty of room to mount one (or more if you were so inclined) of those smaller deep cycle batteries like they make for kayak trolling motors. Weld up a simple frame that you could slide the battery into and mount it to the bed; easy enough to do with the Tacoma's polymer/glass (whatever it is) bed.

Charging it should be simple enough I'd think, similar to any other dual battery setup.

I only want it for use as a house battery which wouldn't get used that often- powering a couple of LED lights on occasions such as loading boats, recharging a tablet or phone and maybe plugging my laptop into if I want to watch a movie.

Just scheming more crap for the truck which I probably don't need.
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https://www.torklift.com/automotive/hiddenpower
 
It looks like those Torklift brackets are for mounting on a frame, the Tacoma doesn't have enough room underneath for that which is why I was thinking about something smaller that would fit in the unused space between the quarter panel and the bed. I've seen a few slim batteries that would work but they are very expensive, ex. https://www.westmarine.com/buy/mastervolt--slimline-compressed-agm-batteries--P010976439

Welding up a bracket is the easy part and a backing plate should keep it secured without cracking the Tacoma's synthetic bed; I don't jump my truck or anything hard like that.
 
You sure those would fit? Unless you're thinking of standing then up on the 11" side.

Specifications 12/185

  • Group Size: Specialty
  • Terminal Type: M6 (6mm bolts)
  • Amp Hours (Ah): 185
  • Cold Cranking Amps (CCA): 930
  • Marine Cranking Amps (MCA): N/A
  • Reserve Minutes: N/A
  • Weight: 113 lbs.
  • Dimensions: 22"L x 5"W x 11"H
  • Warranty: Two-year warranty
 
I don't have my measurements from the truck in front of me and I may have linked to the wrong battery, I just clicked on the first slim battery that I saw on their website as an example of the style. There are other sizes out there that have the same general shape and I know I found at least one that would fit but I doubt the CCA was as high. There are some small marine/deep cycle batteries made for fishing kayaks as well that might work for short term use if the fridge were plugged in to the truck's charging system during the day; probably not a good choice for longer than overnight use though. I'd have to crunch some numbers to see how well that would work and honestly, I'm not that good with figuring voltage draw.
 
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