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MOAR Power, More Redundancy - Dual AGM Battery Install

June 18, 2019.

Well, this post is a long time in the making. In fact, I assumed this was a project I'd get taken care of in the dead of winter, since much of it would be done in the wood shop, and none of it required the truck to be outside in the rain and cold.

But like many well-laid plans, mine got comfortable and took a six-month nap. So let's start at the beginning...

My Battery History

To date, I've only had to replace the battery in the truck once. I did that back in 2011 after owning the truck for 11+ years, but I've known since I got the fridge that I was always sort-of pushing my luck. I mean sure, the 50qt ARB fridge will shut off when the battery gets below a certain voltage, and sure, I had a DBPOWER Lithium Ion battery pack that could (theoretically) jumpstart the truck, but still. So, when my Toyota Truestart battery started going out on The Re-Tour in the fall of 2018, I knew the time had come to upgrade the battery system.

My first step - of course - was to jump on a TacomaWorld group by for two, Northstar AGM 24F batteries. This was in November - the perfect time to start a winter truck project. Or - as it turned out - to exercise the UPS delivery driver. See, the first two batteries that were delivered were not size 24F, but were instead size 35 batteries. The seller was great about it however, and within a couple days the UPS driver was back to drop off two more 70 lbs batteries, and take the original ones with him.

Unfortunately, upon opening the second batteries, I found that the posts on one of them had been crushed during shipping. Well, that was no good, but a quick set of emails to the seller and I was left impressed. While a replacement 24F was going to take a few weeks due to being on back order, everything was taken care of as quickly and professionally as I could have asked.

Finally - in the middle of January - I had my new power packs.

Since at that point I was running a spare battery from Mike @Digiratus in the truck, I promptly replaced that with one of the Northstar batteries and assured myself that the second wasn't far behind. And then I started contemplating where to put the second battery.

Where to Put the New Battery

My contemplation took months - and brings us to the present day. Nearly. See, there were a few places I could put the battery:

  1. Under the bed, where the spare tire was originally mounted. This was where I thought I wanted the battery - in a custom fabricated steel box - but I didn't love the idea of putting that weight behind the axle or having the battery in what seemed like a reasonably vulnerable - and hard to seal from the elements - location.
  2. My next attempt was above the frame just in front of the rear wheels. This was suggested to me by a couple of folks and would keep the battery further forward and be less vulnerable. It would however still have the "exposed to the elements" problem, and of course when I finally measured, it wouldn't fit.
  3. In the cab, behind the passenger seat. I originally shied away from this since I wanted to keep the inside as spacious as possible, but it would solve the problem of the elements, and keep the battery further forward. My final admittance that the truck is no longer a daily driver and is really just an adventure vehicle sealed the deal. This is where the battery would go.

Parts - More Than Just Batteries

At that point, I also had to gather all the other parts that go into a dual battery setup and account for just as much cost as the batteries themselves. I'll list what I used here, since it's likely to be similar for just about anyone planning to add a second battery to their Tacoma.

I purchased everything over time - a sure way to make the cost less noticeable - and by June I was finally ready to get started with the install.

Building a Cabinet

I knew I needed to secure the battery well within the passenger compartment - I didn't want to have it flopping around on the trail, much less if I ever got in an accident. And, I figured that this was a good time to build a bit more than just a battery box - I could also build a place for the fuse block, and some other odds-and-ends that were previously just floating around behind the front seats on our trips.

The problem of course was that there are essentially no 90° angles in the extended cab portion of a 1st gen Tacoma, so building a cabinet would be a bit of cut-a-piece-at-a-time affair. So, I found a scrap piece of ¾" plywood and got started.

Of course, I also needed somewhere to attach the cabinet, and my goal was to be as nondestructive as possible. As such, I hoped I could use the two captured M8 nuts that secured the small fold-open shelf, and one of the rear M10 seat belt anchors - three points that I thought would likely be enough to secure everything well.

Eventually, I had the minimum number of prototype pieces cut and assembled to have confidence in the design and knowledge of the various angles I was working with, and I moved on to a more precise plan in Sketchup - really, just as a way to learn the 3D modelling tool that I'd never used before.

And then, it was time to get started on the actual cabinet. I happened to have a nice piece of ¾" prefinished A1 grade maple plywood hanging around from some previous projects, so I broke out the Makita track saw and started breaking down the pieces.

To strengthen the joints, the next step was cutting dadoes and rabbits in various locations to accept mating pieces, as well as cutting an access hole for the storage compartment that would eventually be below the cabinet (and that I still wanted to access). Then, it was time for basic assembly.

The cabinet was definitely starting to come together - the battery would sit in a compartment on the right, my small recovery and air-up kits in the bottom left cubby, the wiring and fuse block in the middle left-cubby, and then there would be two shelves on the top to store various items I take on my adventures.

At this point, I'd planned to be done - but something was nagging at me. I realized that I can't leave a project "mostly finished" - in this case, the exposed plywood edges are just "undone." So it was back to the table saw to make some edge banding, and of course a finger-jointed, pull-out drawer - for the electronics that would be housed in the middle compartment.

Again, I planned to be done here until I realized that I was still rushing. The edge banding and a few pieces of solid maple needed finish in order to look right next to the prefinished plywood. So, a couple coats of wipe-on polyurethane were in order before calling the cabinet done.

Installing the Cabinet

With the cabinet put together and all the necessary parts for the electronics already in hand, I had no excuse for procrastinating the actual install. But that didn't stop me! Quite the opposite - I procrastinated a good week or two, building a few bed racks for folks, and helping a friend with a 4Runner storage system on his truck. Oh, and there were wheels to be painted.

Turns out, I can procrastinate anything!

Eventually though, I had an upcoming trip where I knew the truck would be sitting all day, and the fridge would benefit from a second battery - so I broke down and got started with the install.

Up first was making sure the cabinet was secure. The two lower mounting points were easy - a couple longer M8 bolts could secure the cabinet to the captured nuts - but the upper mount, to the seat belt anchor, was going to need a custom bracket. Using some of the 3/16" aluminum I had laying around from the 4Runner roof rack, I set about making a bracket to accept a carriage bolt that would pass through the bottom of the cabinet to keep it in place.

Bracket made, it was time for cabinet installation. Were my measurements correct? Would everything line up? Or, would it be a case of measure once, try it, and measure again? I prepped the area and then moved the cabinet into place. And low and behold - everything lined up the very first time! Sweet!

And Finally - the Battery!

Cabinet installed, there was only one thing left to do - install all the electronics. I mean, that's what this whole project was about - right? The way I saw it, there were a few steps - first, removing the circuits from the Bussmann RTMR that I'd be powering off of the secondary battery, then, running the two main power wires that connected the two batteries through the Blue Sea ML-ACR, and then wiring all of the circuits up to the Blue Sea circuit breaker and 12-circuit fuse block. Oh, and of course, there was turning everything on!

Removal of the circuits from the Bussmann was - of course - easy. That's the whole point of having a Bussmann, after all. Perhaps most rewarding was removing all of the negative wires from the ground screw I'd been using in the engine bay.

Next, I ran the 1-0 gauge man-that's-big-cable from the starting battery, around the engine bay, through a grommet in the passenger side of the firewall, along the door threshold, and up into the cabinet. I was quite glad at this point to have use the mesh sleeving, as it made me much less nervous as I pulled the wire by and through the various crevices.

At that point, I could start using the 16-ton hydraulic crimper to attach the lugs onto the ends of the cables as well - something I'd hesitated to do until I knew the lengths I needed, and gotten the cables through the various grommets.

I could smell the finish line as this point. As I routed the accessory circuits for the fridge, ham radio, and CB radio to the fuse block, I was sure that I'd be done in 30 minutes. This of course was a gross underestimation, but I could definitely see the light at the end of this project. Assuming it all worked when I flipped the proverbial switch.

The only thing left to do at this point was to wire up the switch that controls the ML-ACR. this switch allows the operator to either join together - or isolate - the batteries as charging conditions change, and also allows for an automatic mode with the ML-ACR handles the connection itself.

And with that, the electronics - at least for now - were complete, and it was time to hook everything up; hopefully not electrocuting myself or burning up the truck in the process. So, I attached all the appropriate cables to the starting battery, and did the same for the secondary battery, and then connected the two through the ML-ACR.

And it all just seemed to work! I'm not sure it was a miracle, but I sure wasn't complaining.

Wrapping Things Up

With everything working, I got things cleaned up - there were still a few things to wrap up, but those would have to wait for another day - because in less than 12-hours, we were headed off on an adventure...

...(a few days later)...

Wrap up is complete. A small box to hold the ML-ACR switch, and a hold-down for the secondary battery are now in place and everything is working swimmingly.

Plus, @mrs.turbodb loves the fact that she's got a place for her bag on trips, and I like the perfectly-sized camera storage shelf atop the battery compartment. All-in-all, a successful project - assuming it works that is...

3 Comments

  1. Rich V
    Rich V June 27, 2019

    Kinda sad to lose that interior storage space but function trumps form and the ability to lay the seat back for a nap! It would not fly in my squadron..many things that "work" usually don't! Your Mrs. is more flexy than mine 🙂
    Nice work sir!

    • turbodb
      turbodb June 27, 2019

      Thanks! We don't lean the seats back for naps, and I think it could still make it most of the way back even with the cabinet. Usually there's so much stuff behind the seats on a trip, that the cabinet might actually let it lean back further! hahahaha 🙂

  2. Jim Battagin
    Jim Battagin June 30, 2019

    you are having WAY too much fun! UJ

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