Auxiliary / Second "House Battery" in Bed - Help Needed

Hi folks, I'm in need of assistance with a project of mine. I recently bought my Tundra with the goal of turning the bed into a camper. I have a cap on order, and am getting ready to build it out.

I want to bring some electrical to the bed in the form of a second battery / "house battery." Ideally I would charge it up at the house before I leave for a trip, and it would be topped off by the truck while out. Either through a DC-DC charger or through a 12v cigarette outlet? And having the option to add solar down the line.

Now I'm fairly handy, but when it comes to electrical work I'm a little lost. I've attached a picture of what I want to accomplish and would appreciate some guidance into how I can make this happen. I'm not sure where and what fuses to add, gauge of wire, if my battery capacity is enough etc? I'm currently looking at a 100ah lithium battery, or if I go AGM, I understand I would need 200ah. In the winter, the priority is running a 12v diesel heater. It draws 10-15 amps at startup for about a minute, and then while its running on low ~1amp/h. From what I've read budgeting 20 amps / night should be quite conservative.



I will be having an electrician friend help me out with all of this, but I wanted to get some opinions here, and also that way I don't look like a complete moron. I was looking at some of the goal zero and jackery options, but it seems to be more cost effective to build one on my own.

 

Save yourself a whole bunch of time and effort and buy this and stuff the largest battery you can in it.
Unless you are just doing a ton of camping every weekend and like projects it is not really worth all that effort.
Newport Vessels Trolling Motor Smart Battery Box Power Center with USB and DC Ports, Black, Medium

$65 Newport Trolling Motor Smart Battery Box Power Center with USB and DC Ports

https://smile.amazon.com/dp/B01AE2TG7G?_encoding=UTF8

Or buy a Jackery

 

Unfortunately that won't quite meet my needs. It would be nice and save a bunch of time.

I do a fair bit of camping. I'm out most weekends and do quite a few 4-5 day trips. I'll be using the truck as more of a basecamp style camp so I'm hoping to make it as comfortable as possible. I definitely want to have an 110v AC outlet, and a larger capacity. More similar to an RV battery setup.

 

I’m planning to do something similar. There are so many options but the path of least resistance (aside from above or GoalZero, etc) seems to be a Renogy DC to DC charge controller. You can start with one battery and add additional as needed.

This is a sample schematic that I found on some RV site. The wires ‘to alternator’ can go to the car battery. You made need a jumper, I forget if the Tundra has a “smart” alternator. In the future add solar panels.

Just remember, connect the battery to the charge controller first. And find a cheat sheet for sizing wire gauge and fuses. YouTube search this charge controller as well and you’ll be a pro in no time...

 

Redarc BCDC charger is all you need. It has solar input built into it.

https://www.tundras.com/threads/dual-battery-charging.94367/

 

Either redarc bcdc or Renogy mppt dc-dc will suite you well.

Main difference between the two (other than build quality) is if renogy has both inputs (solar and alternator) hooked up, it splits the input 50/50 down the middle. So say you get the 30amp version, the most you can pull from solar is 15 and 15 from alternator. Some people wire in switches so they can make it seem like solar is disconnected and they can draw the full 30amps off the alternator while on long trips.

redarc supplements. So say you go with the 25amp version (I believe that’s one) and you are only pulling 5 amps from solars, it’ll supplement the other 20 amps from the alternator. All in all, it’s not really that big a deal unless you are doing massive discharges every day/night buts it’s something to consider. I’ve had my renogy going for 6 months now, no problems. Good luck!

 

After doing some more research I'm going to go with the renogy unit, probably a 40amp DC-DC with the MPPT. The redarc does seem like a nicer unit with the supplement charging, but for my use I don't think it is worth the large difference in price.

Next I need to decide on a battery. 100ah lithium or 200ah agm / lead acid... also need to choose an inverter, 1500w? plus figure out breakers and fuses

 

Renogy gives fuse size recommendations in their instructions (can be found on their website) and quite a few people have their setups on their builds. Smslavin has a good write up in his build similar to yours if you want to check his out. As far as battery, I’d go lithium simply for the weight savings. If you do go lithium and live in a colder climate, and plan to have the battery in the elements 24/7, just make sure it has a heating function. The older Renogy’s don’t and you don’t want to discharge a cold lithium battery. Will Prowse on YouTube answered 90% of my questions. Wish I had taken his advice and gone with a SOK battery. Best bang for the buck lithium for sure

 

Coming in late to the thread, and to be honest, only skimmed the other posts...

If you're just running the diesel heater (and a fan, lights, etc); are you really sure you need 200aH for an AGM (100aH LiFePO4)? Are you planning on being parked for those 4-5 day stretches? Also, how much solar are you planning on adding?

My questions are just based on my own experience. I'm running a 102aH AGM in the bed that is charged from three sources (alternator, solar, and AC charger). The aux battery powers everything (except the winch) that has been added to the truck (including all the in cab accessories). Constant draw loads include an ARB fridge, the victron gear that is always powered (for bluetooth), and a wireless light controller (for lights inside the topper). Realistically, when the fridge isn't running, constant draw is somewhere in the region of 3-7 watts.

Our camping style usually involves us only spending about 14-16hrs parked, but even when spending two nights (40hrs) parked with ground lights at night, USB chargers almost continuously, roof fan on low continuously, etc. the lowest SoC I've seen is somewhere in the neighborhood of 78% (~25aH used). That was before the addition of our solar panels.

My setup consists of: Northstar 27F AGM (main battery), connected via a Blue Sea ML-ACR (and 2/0 wiring) to a Northstar 31 AGM aux battery (in the bed). Charging voltage was increased via a GM diode replacing the ALT-S fuse. For AC charging I have a Victron IP67 25A AC-DC charger with a plug in the rear bumper that is wired to the aux battery, however, since the ML-ACR senses voltage bi-directionally, it will connect the two batteries while charging and make sure both are charged. Generally this is only used in my driveway. For solar I run two 100w flexible solar panels on the roof of our AT Atlas, wired to a Victron SmartSolar charge controller. I also have a 500VA Victron inverter as needed, but our laptops charge off of USB-PD instead.

To give any sort of similarity to your needs, we run a Truma propane-fueled heater, which draws around 1-1.5A while running through the night; and on a recent shakedown run of being parked with the heater on for 14+hrs found a very minor overall drop in battery SoC the next morning.

Now back to your other questions; LiFePO4 is phenomenal, but if cold weather is expected, be prepared for the problems that may arise. Battle Born has the heated batteries, but even those are only good to -4F I believe. From what I can gather, they are much more ideal for a climate controlled space.

 

Hah!

Electrical starts on this post: https://www.tundras.com/threads/mallcrl-2-0-21-sx-double-cab-build.82563/#post-2143466

And continues on this post: https://www.tundras.com/threads/mallcrl-2-0-21-sx-double-cab-build.82563/page-3#post-2403700

And solar here: https://www.tundras.com/threads/mallcrl-2-0-21-sx-double-cab-build.82563/page-3#post-2492861

 

Thanks for all the replies. 100ah is probably a bit overkill, but I would like to be able to run the diesel heater, fan and charge phone for 3 nights without having to charge or worry about running out of power. At the beginning I won't be adding any solar, all the charging will be done at home and topped off with the DC-DC. We also don't get a lot of sun here over the winter, and I do spend a lot of time winter camping. So I'll have to look at the limitations of lithium batterys for sure.