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

Robert

Adventurist
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.
 
So if it's just for small things occasionally, why even bother with the outrageous expense of dual battery, and all the effort to build a storage place for it?

Just upgrade your starting battery to the largest AGM you can fit, and be done with it.

It amazes me why people still think you have to have a dual battery system. A stock battery upgrade will go far longer than any dual battery system will, I guarantee it.
 
Well I've got a nice starting battery, I already have a dual battery setup but never got around to installing it, the small marine batteries are like $50 and mainly- because I like to tinker with crap. It gives me an excuse to design something, weld it up and install it then probably rarely use it. Since I usually travel alone though I like having a second battery and the marine battery I currently use is large and heavy and takes up room in the back. A small marine battery, most of them are about the size of a lawn mower battery, ought to give me at least a couple of cranks if I needed it. I've already got the Taco lean so I really don't want another battery next to the factory one and my ABS setup consumes the space on the passenger side that would otherwise be perfect for one. Freakin' Toyota engineers wasting engine compartment space:
:mike Basically, because I can I guess.
 
Freakin' Toyota engineers aren't the problem. Overthinking Overlanders are the problem!

The problem with the dual battery setup is this: You THINK your alternator can charge a second battery as well as it charges the first, but this is incorrect for a number of reasons. Your alternator is designed to run the vehicle systems while in operation, and the energy left over is intended to recover the starting battery from what it lost while starting your vehicle (very little loss actually), and keep that battery topped off, so that it's ready to go next time you start.

Adding an auxiliary bank of batteries, usually deep cycle variety, and then using them to depletion, causes a great problem. Because the only way to get them back to full charge is TIME. I don't care if you have two DC to DC chargers and a Generator. If you drain a 100 Amp Hour battery, you'd better not expect it to fully recharge in less than 10 hours. PERIOD.

So that means after your 3 day camping trip that drained your auxiliary battery, you'd better take the long way home if you want that battery charged back to full by just your alternator. AND/OR put an intelligent battery charger (CTEK MUS4.3 or equivalent) on the aux bank when you get home.

Why? Because while marine/AGM batteries are made for very deep draws, what they expect in between those draws is return to full charge. NOT doing so results in a dead battery YEARS before its expected replacement date.

Having done this for a living for long enough, I have customers who call up, upset their dual battery system isn't performing to their expectations. And the problem isn't the system I built, it's their expectations, and not having a clue how to maintain their system, and live within its limitations.

I've operated on a single battery installation for 6 years without issue or replacement. I use a solar panel when I'm camping; If I'm sitting still, and there is daylight, my panel is up and keeping my battery topped off all day long, because all I care about is running a few camp lights for a couple hours and carrying the fridge through the night. In the morning, I adjust the panel toward the sun, and within a couple hours, the loss from running the fridge is refilled, and the panel will keep it topped off all day again.

I don't run my fridge when I'm not in need of it. It doesn't sit in my driveway keeping a couple waters cooled all week long. Although it could if I set my solar panel up.

Can my single Group 31 battery run my fridge for a weekend without needing charged? Under ideal (not too hot out) conditions, YES, absolutely it can. But WHY would I want to abuse my battery like that if I don't have to? The Odyssey Group 31 is a 12 year battery if taken care of properly. But I have customers killing them within TWO YEARS because of abuse.

My single battery upgrade AND a solar suitcase saved me over $1000 compared to what my customers had installed for dual batteries. Proper mounting cages that don't fail under even the smallest of accidents are expensive (batteries are heavy, add inertia and they get heavier and become projectiles), DC to DC chargers or smart solenoids, cost of the second/third battery, and paying someone to wire it all up adds up quick.

If someone comes to me with the want of dual battery, they'll need to show why they need it; That their power consumption exceeds the capacity of the upgraded main battery, and that they're willing to go the distance to properly maintain the charge requirements of the auxiliary battery. I'll no longer install it, and then listen to people complain it didn't last as long as they thought it would.

Just because you can, doesn't mean you should.
 
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@Mitch Very interesting point on the charging side of things. Do you know what a realistic output is from the OE Toyota (or other similar OE) is?

On my Ford I rely on the alternators charging the house batteries. But I generally do long enough stretches to refill them (or most of the way). It does get plugged in at home to keep them topped up.

Here is the data from the shunt at the house batteries, while on the freeway. This is dual 120amp alternators.
43231376734_6af45c7f8e_b.jpg


I put the tray in my 4runner for dual batteries ~8 years ago. Still no battery in it..... I do run a "priority start" which has saved my ass a time or two when the fridge tried to suck the battery dry.
 
I'm running a Group 31 Marine (DieHard/Odyssey AGM) as my house battery. It happily runs the fridge, water pump, and lights for several days.

It's connected to an alternator with a cheap T-Max controller + solenoid, but mostly it's maintained by a solar panel and a 45A charger when on shore-power. The solenoid connection to the starting battery doesn't do much to keep the house battery charged in the field, but it does worth the other way to make a convenient way to make sure the starting battery is also kept topped up if my van happens to sit for a few weeks. Charging voltages from either the solar panel or shore power charger are enough to kick in the relay so that both the starter and house batteries are charged.

I'm currently running with 60w of solar on a PWM charger, and I find that's sufficient for "indefinite" power usage from the house battery if and only if I'm diligent about keeping the panel in full sun. I plan to upgrade to 100w and an MPPT charger, just to pick up a little margin.
 
Both of you are using MULTIPLE methods to keep your auxiliary battery charged up.

FACT: Your alternator, regardless of size, is not going to cut it. We just don't (TYPICALLY) drive far/long enough between draws.

CONCLUSION: If you're using SOLAR/Shore Charging/ETC (anything in addition to the alternator), then isn't just ONE battery sufficient? Why go through all the cost of another battery: An Odyssey PC2150-31M is over $400, the costs of the DC to DC charger or solenoid system: $200 to $500, and proper trays: $200-$500, when a simple main battery upgrade and solar saves over $1000.00?
 
@Mitch Very interesting point on the charging side of things. Do you know what a realistic output is from the OE Toyota (or other similar OE) is?

On my Ford I rely on the alternators charging the house batteries. But I generally do long enough stretches to refill them (or most of the way). It does get plugged in at home to keep them topped up.

Here is the data from the shunt at the house batteries, while on the freeway. This is dual 120amp alternators.
43231376734_6af45c7f8e_b.jpg


I put the tray in my 4runner for dual batteries ~8 years ago. Still no battery in it..... I do run a "priority start" which has saved my ass a time or two when the fridge tried to suck the battery dry.

It honestly doesn't matter, but the Toyota alternators range from 70 amp to 140 amp.

Again... It doesn't matter how many alternators you have. Voltage is instantaneous, CAPACITY is only replaced by ABSORPTION charging, and absorption only happens over time. You either don't have enough solar to support the battery bank vs. its' draws, or you just don't drive 14 hour days.

Looking at the image you attached there, the damage is going to come from not being at 100% before you put another deep draw on the battery bank. There's much more to the complexity, but that's the basic gist of it. It's also important to correctly wire your draws if there are more than one battery in your auxiliary bank.
 
It honestly doesn't matter, but the Toyota alternators range from 70 amp to 140 amp.

Again... It doesn't matter how many alternators you have. Voltage is instantaneous, CAPACITY is only replaced by ABSORPTION charging, and absorption only happens over time. You either don't have enough solar to support the battery bank vs. its' draws, or you just don't drive 14 hour days.

Looking at the image you attached there, the damage is going to come from not being at 100% before you put another deep draw on the battery bank. There's much more to the complexity, but that's the basic gist of it. It's also important to correctly wire your draws if there are more than one battery in your auxiliary bank.

Agreed, but more amps means shorter drive time to charge. I try to hit 100% every time but it depends on how long we have been sitting vs the drive time. I generally get there, but not always.
 
@java230 More amps doesn't exactly equate to shorter charge times, because the battery is only capable of drawing so many amps. With your dual alternators, you've assured you're going to hit that maximum, but the battery will hit its amp absorption limit, and from there only time can do the work.

The best effort spent here, would be to provide more solar amps into the batteries than you are using, leaving you with a net gain to keep them topped off throughout the day so that your much lower amp load at night is maintained by the batteries.
 
@java230 More amps doesn't exactly equate to shorter charge times, because the battery is only capable of drawing so many amps. With your dual alternators, you've assured you're going to hit that maximum, but the battery will hit its amp absorption limit, and from there only time can do the work.

The best effort spent here, would be to provide more solar amps into the batteries than you are using, leaving you with a net gain to keep them topped off throughout the day so that your much lower amp load at night is maintained by the batteries.

Yes, but getting to max absorption rate (with a big bank like mine or a dual battery even) is very hard to do with any OE alternator is what I am hearing you say (from the original post about how dual batteries are a bit silly). No idea what mine really is, but it always seems to settle around the 70-75amp mark like above. Maybe thats max I can get from the alternators or max absorption. Obviously it tapers off as charge % goes up. I rarely get below 80% or so. In theory I should be able to go 5 days with zero charging before hitting 50%SOC in the winter and I try to avoid that!

I agree solar would be great, and its in the works, but I can't rely on that when its under snow in the winter.
 
Both of you are using MULTIPLE methods to keep your auxiliary battery charged up.

FACT: Your alternator, regardless of size, is not going to cut it. We just don't (TYPICALLY) drive far/long enough between draws.

CONCLUSION: If you're using SOLAR/Shore Charging/ETC (anything in addition to the alternator), then isn't just ONE battery sufficient? Why go through all the cost of another battery: An Odyssey PC2150-31M is over $400, the costs of the DC to DC charger or solenoid system: $200 to $500, and proper trays: $200-$500, when a simple main battery upgrade and solar saves over $1000.00?

Agreed that the alternator does not contribute to my charging solution (as stipulated in my first post). Like I said, the main purpose of the battery relay/controller is to be able to top off the starter battery from existing charge sources.

So why isn't a single battery sufficient? Because I want to be able to sit for 3 days, in a remote and possibly solar-disadvantaged spot (tree cover, clouds, rain), and still be able to guarantee that the van starts on the fourth day.

I am not aware of any starter battery that will deliver that capability - at least not that would fit in the engine bay of an Astro van (Group 78). I average about 15-20AH consumed per day, in nominal weather. If the sun is good, I can put most of that back. If the sun is bad, I can't.

Coming home after a long weekend with the 100AH battery at ~50% DOD is just fine with me because I've got shore power and can take as long as I need to recharge during the work week.
 
@Herbie By stating "both of you", I was leaving you guys out of my argument. With some information thrown in for others. Also I didn't say starter battery, I said upgraded battery. Your van is a special case simply because its a van, and there isn't room for a whole lot of upgrades under your hood. So you gotta do what you gotta do.

I'm not saying that dual battery isn't necessary, sometimes it is, for 95% of the folks, it isn't.
 
Toyota engineers may not be part of the problem when it comes to the charging system but they are when it comes to efficient use of underhood space (yeah, I know that doesn't really seem to occur to them). They're also responsible for the utter crap ABS system on Tacomas but that's another story. They could have mounted it somewhere better that wouldn't eat up room I could use for other stuff like air compressors, batteries, tool boxes, etc. especially knowing how their market tends to modify their products. :p Besides, that National Luna system I've got sitting in storage costs good money right?

I've been using a separate marine battery stored in the back of the truck for my Edgestar and cooling fan. I'd charge it at home or when I had access to 120v but it's given up the ghost after probably ten years including sitting unloved for several of those while I was out of the country. I was thinking of other options, primarily for overnight charging of small things and running a 12v fan, but also occasionally powering the fridge overnight (nope, I haven't done the calculations on that yet); I know it would be absolutely worthless trying to run the Warn XD9000 on the front of the truck. Solar is a great option other than my tendency to carry boats on my roof rack; I guess I could build a Prinsu style rack over the cab to mount them but I like not having stuff over the cab creating wind noise. Also not a fan of taking yet another hit on my already crappy gas mileage. A fold out style would kind of sort of work if I was staying in one place during the day but I tend to move around a lot.

Oh well, it'd probably be cheaper and easier just to buy one of the LiPo starter packs and stash it for emergencies.
 
Solar is a great option other than my tendency to carry boats on my roof rack; I guess I could build a Prinsu style rack over the cab to mount them but I like not having stuff over the cab creating wind noise.

I decided not to mount the solar panels on the roof. What if I want to park in the shade? The camper shell on the back and the interior are going to get balls hot sitting in the sun. The fridge will then have to work harder to keep everything cool. Fans will have to run longer to make thing bearable. Na.

2 50W panels in series or a single panel depending on power needs. About 18' of heavy 10g to the charge controller and 6' of the same with alligator clips for the starter battery. That should be enough to keep them in the sun and me in the shade.

2 SunPower 50W $119 each on Amazon
 
Pretty cool panels and smaller than I would have expected. Do they work well and how do you store them? Are they easily scratched?
 
Pretty cool panels and smaller than I would have expected. Do they work well and how do you store them? Are they easily scratched?

I just got them so I can't answer how well they work. I did pick these because they are the same manufacturer that Overland Solar uses. Cleans with Windex. And the specs are right. My guess is that these are a previous generation. The current spec sheet has slightly better performance. It's a fairly hard plastic so it will a little effort to scratch them. One of the intended uses are to be glued to curved external vehicle surfaces.

I store them in an artist's portfolio. If it's good enough to keep paintings and drawings undamaged it should be good enough for the these.
 
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