Dual purpose battery

I want to double my amp hour capacity of my travel trailer but don't want to add more weight. So I'm considering installing a dual purpose battery in the taco, such as Interstate's https://www.interstatebatteries.com...Line=rv&subcategoryKey=&ignorecategoryid=true. This is supposed to be a deep cycle and a starting batt (aka dual purpose). When camping I would leave the truck plugged into the trailer so I would have twice the capacity. When I camp I have a 150w solar panel recharging the camper which would also feed back into the truck battery.

What are your thoughts on this?

 

Both batteries will equalize unless you keep them isolated .

Meaning if you discharge the system to fast your truck won`t crank

 

@Wyoming09 that makes sense, I’ll do more research on that. Generally I keep a very close watch on the discharge so in theory if both batts are designed for a discharge state than it would be ok if I don’t let them drop too low - but would still be able to crank.

 

A. battery bank switch will give more versatility by being able to select battery 1, 2 or both for charging and discharge.

 

From what I've read a dual purpose battery isn't truly able to deep cycle like an actual deep cycle battery. You can only partially deep cycle it and not as many times.

Also, with using your starting battery as your house battery you risk getting stranded by draining your starting battery. If you only camp with others or you always have power available or you carry a jump pack you can stretch this. The down side is you'll be deep cycling your dual purpose battery, which doesn't handle deep cycling well, and will kill it.

That battery you linked to is 70 pounds. That's a lot of weight in the stock battery location. There have been several TW members, myself included, that have suffered damage to their trucks from heavier batteries in the stock battery location. I think a lot of these cases have been largely due to off road use, like mine. So if you don't off road you should be fine.

There is no real way to double amp hours without adding weight. Lithium would be a great way to go but it's super expensive....for now at least.
How about reducing your power needs?
Speaking of which..what are your power needs?

There's a ton of good information here as well -
https://expeditionportal.com/forum/forums/power-systems-12v-solar-gen.48/

 

a little bit of $ but IMHO light years better... a Honda EU-1000 about 40 lbs and $800.

 

And you can use it at home for power outages etc.

 

What is your plan for connecting the Truck battery to the Trailer?

 

@otis24 good insights, thanks. I’ll check out that link.

I’ve reduced power needs to very minimal. We most often dry camp, boondock or whatever you want to call it. My power needs are not much really, I’ve gone 7 days with only a 100amp hr battery but I’m looking to add another Maxxfan and that would pull a bit too much.

I have a good solar setup, I might just double it. I have a generator but prefer to never use it....the sun is free, quiet and the smarter option imho. Just takes planning. I think this discussion made me realize the smart thing would be to double up on solar and I’ll have what I need.

@YF_Ryan 7 pin trailer connector

 

The 7 pin trailer connector has a VERY small gauge wire. The voltage loss over that run will be quite a lot. That wire is only really good for a tiny trickle charge or the smallest of power draws.

If you want decent power, you'll need to run heavy gauge cable from the truck battery to the trailer separately.

 

And in regard to just doubling your solar, that sounds like a MUCH simpler and cost effective idea!

 

DO NOT USE THE BATTERY YOU NEED TO START YOUR TRUCK TO POWER YOUR TRAILER LIGHTS!!!!

Do not connect your starter battery to your trailer power except when towing. That 7 pin connector is only good for keeping the trailer battery(s) topped off. It's not going to charge a dead battery even with several hours of driving (with higher amperage from the alternator).

If you want more capacity without extra weight, get a lithium battery.

That said, I have a 18' travel trailer and my 100W solar panel is more than enough to run everything I need indefinitely. How much power are you using?

What trailer do you have? What are your power needs?

My travel trailer is a dual battery setup. Well, it is now. I didn't notice the extra weight when I installed it, lol.

 

I don't live in the PG&E service area, so don't need to worry about that.

 

That brings up a good question for OP. @life as ben do you live in an area with power outages that you could benefit from something like a generator so it has more than one use?

Hmmm....I should figure out how long I can run the fridge in the house off my truck....200 watts solar, 230ah of batteries, 1500 watt inverter. We have a generator but why not have a back up for the back up?

I'm right in the heart of some of the PG&E outages in the Santa Cruz Mountains. We had like 6 or 8 days total power outage this year. We usually lose power at some point in the winter due to weather as well.

 

OP already said he had a generator (didn't say what kind). Just wants to avoid using it.

When power went out for me, I actually took all the stuff outta my freezer and tossed it in my Dometic for a couple days. Never had to worry about losing all that frozen cow.

 

Yeah, that sucks. I have some friends who lost their homes in some of those fires. Then many others didn't have power for over a week. And PG&E is trying to blame everyone but themselves.

Anyhoo...

So a typical residential fridge is on the order of 6.5 amp draw, (x120v = 780 watts).

Your battery: 230Ah x 12v= 2760Wh.
For panel: 200W x 12v = 2400Watts

You panel is big enough, but you'd only be able to run the fridge on batteries for like 3.5 hours (2760/780) at night assuming 100% discharge. So really, more like 2.5 hours.

For that, you'd be better off with getting a 2-way RV fridge and run it on propane. Mine can run for weeks on a 20lb tank. That frees up your battery/panels to run all the other stuff that isn't running 100% of the time.

 

I have a heavily modified 2017 Cherokee Wolf Pup. Our power needs are lights (all LED's), two Maxxfans, 12v TV sometimes and the water pump. I carry my Ego 7Amh and 20v Dewalt batteries with me for all other incidental needs like phones, personal fans, etc.

I would upgrade to a larger battery but I'm trying to shed every pound I can so I get a little better towing. A lithium is just not in the budget. I'm removing the 75lb A/C unit this week, never really use it and can put it back for trips when needed.

 

Are you noticing that you consistently drain your battery overnight, and can't get it fully charged the next day via solar?

If not, you have nothing to worry about.

I have a larger trailer, and a smaller solar setup than you. Same dual fans, stereo, pumps, LED lights, phones, all that stuff. I have a dual battery (AGMs) setup but honestly probably didn't "need" it. My main problem was my tiny 40watt solar I had left over from my popup trailer. I've been boondocking for over a week with my current 100watt setup and the battery level hardly ever budged. You hardly use any power at night, so the majority of your power comes from solar. Dual batteries just help if there's an extended period with no sun.

With a 3000 pound trailer, I challenge you to notice a difference in MPGs or drivability with a 2nd AGM battery.

Just don't ever connect your truck battery to the trailer as a way to get extra capacity. That's a really terrible idea. Leave the truck battery for starting the truck.

 

No, not draining it overnight but after several days of continuous Maxxfan running with intermittent water pump etc. the panel isn't quit enough to keep it topped off completely. If you throw in a few days with little / no sun it can get close to needing a charge. I want to add another fan and keep both running during hot days/nights so thinking ahead...

 

I recommend a portable solar panel if you don't have that already. I see a lot of people hard mount them on their roofs. The best place to park is rarely the best place for a solar panel (shade, lol).

I splurged and got one that folds in half, so basically 2 50 watt panels and an adjustable bracket so you can face it directly into the sun. You have to keep track of it and move it every few hours for max watts, but you'd be amazed at how much more power you get just form facing it into the sun rather than just flat on a roof rack or something.