Relocating Starting Battery (1 Viewer)

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Joined
Dec 30, 2013
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Location
Vienna, VA
I'm in the process of adding a dual battery system and I'm using the Slee battery trays. The primary battery tray will hold a group 31 and the second battery tray located in front of the air filter will hold a group 35. I was thinking of switching the starter battery to the group 35 battery and the group 31 would be the house battery. This requires the primary battery leads to be extended to the second battery tray in front of the air filter. This seems to be a straightforward change but is there something I'm overlooking that makes this more complicated than connecting new leads and running them to the new battery?

Cheers
 
I'm in the process of adding a dual battery system and I'm using the Slee battery trays. The primary battery tray will hold a group 31 and the second battery tray located in front of the air filter will hold a group 35. I was thinking of switching the starter battery to the group 35 battery and the group 31 would be the house battery. This requires the primary battery leads to be extended to the second battery tray in front of the air filter. This seems to be a straightforward change but is there something I'm overlooking that makes this more complicated than connecting new leads and running them to the new battery?

Cheers

I know many on here have done the Group 31 house / starter battery swap, so you shouldn’t have any issues getting feedback from the Mud collective.

I was contemplating this exact thing the other day. A simple pre-fab’d cable replacement kit would make this a more painless install. I’ve fabricated custom length battery cables in the past and it does require a quality/expensive crimper, unless you want to solder slug the terminals.
 
I’m also curious about the best way to do this. I reached out to ES at Ed Martin but no reply.
In his videos you can see a post that is installed behind where the starter batt used to be. Then a battery cable is run from there over the radiator grille area to the new location for the starter.
I was wondering if there was a post there to connect the factory harness to that post. Then a cable from the post to the new starter. This would eliminate the need to cut the factory terminal and harness but also introduces one more point of failure.
 
I'm not going to solder and will go the crimping route. I need to find a good crimping tool...Many of them on Amazon get poor reviews.
 
I'm not going to solder and will go the crimping route. I need to find a good crimping tool...Many of them on Amazon get poor reviews.
I've used this on many terminals from 2/0 to 8g. Five lb hammer helps to cut down on the number of swings.
It's only drawback is it can't be used underhood, it requires a firm surface like concrete.

Amazon product ASIN B00E1UUVT0
 
@bluefin This is something I've been thinking about, too. I have an email out to Slee with a bunch of electrical questions, and this is one of them. From what I've read here, some have tried cutting off the stock battery terminals and crimping up extensions over to the air box battery tray. There was concern about copper oxidation causing starting issues. Then someone suggested a closeable plastic box filled with dielectric grease to prevent this (like something used in underground power cabling). This doesn't seem like an ideal solution at all. Not only could you be introducing corrosion on the leads, but you would void your manufacturers warranty doing it (according to what Toyota has told me).

This BlueSea product looks really interesting. It would solve that problem above. If your relocated Group 35 starter battery died for whatever reason, (and assuming you didn't have a solenoid between the batteries) you could detach the leads from these posts, and pop them onto the Group 31. Do we know what size we'd need (3/8" or 5/16")? I really hope someone with some detailed knowledge can hop into this thread and tell us (@Eric Sarjeant maybe?)
 
I was thinking of leaving the factory battery terminal and installing a post like the blue seas. There are adapters that look like aOEM battery post. And I was looks into seeing I can install the post on the blue seas with a extension wire that goes to the new starter location.

Positive Insulated Battery Power Junction Post Block 3/8 Lug X 16 thread (Red) Amazon product ASIN B00784HYI2
PICO 0844PT Lead Charging Post for 3/8-Stud-Pos & Neg Amazon product ASIN B001QRTXEK
 
@bluefin This is something I've been thinking about, too. I have an email out to Slee with a bunch of electrical questions, and this is one of them. From what I've read here, some have tried cutting off the stock battery terminals and crimping up extensions over to the air box battery tray. There was concern about copper oxidation causing starting issues. Then someone suggested a closeable plastic box filled with dielectric grease to prevent this (like something used in underground power cabling). This doesn't seem like an ideal solution at all. Not only could you be introducing corrosion on the leads, but you would void your manufacturers warranty doing it (according to what Toyota has told me).

This BlueSea product looks really interesting. It would solve that problem above. If your relocated Group 35 starter battery died for whatever reason, (and assuming you didn't have a solenoid between the batteries) you could detach the leads from these posts, and pop them onto the Group 31. Do we know what size we'd need (3/8" or 5/16")? I really hope someone with some detailed knowledge can hop into this thread and tell us (@Eric Sarjeant maybe?)
I would be interested in what they have to say and had not read about concerns regarding copper oxidation. What gauge wire are you planning on running? I was planning on adding a Redarc SBI and BCDC for charging and having the ability to start from the house battery if the Group 35 battery failed.
 
I’m not an auto electrician, but I see three paths to making the auxiliary battery position the starting battery:

1) cut off factory cable ends and use large gauge wire splices to extend the wires to the other battery location
2) install a post (such as a BlueSea power post) where you create a junction close to the factory location (beside the battery, possibly on the fuse box enclosure), mount the factory terminations on the post, make your own extensions to reach the other battery, put one end on the post, and the other end on the battery
3) remove the factory harness elements and build a custom harness that replaces the factory wires and terminations

Any of them could work. I think 3 (full custom harness) is the most elegant solution and most professional way to do it, but is a lot more work. There are multiple wires to replace. You could upsize the wires as needed to adjust for the additional resistance introduced by the longer wire runs.

On the other hand, option 2 (Power post) is the best way to preserve the ability to quickly and easily return to stock. This seems like a better way to go if this isn’t a vehicle you plan to own in the longer term. Or if you want the ability to quickly revert to a stock configuration (like for troubleshooting, for example). You could quickly install a group 27F battery with the factory battery clamps and you are back to the stock electrical configuration in minutes.

Based on videos he’s posted, I believe some variation of option 2 (power post) is the one Eric Sarjeant’s electrical sub does it.

There are probably lots of other options, but these are the ones that jump to mind for me.

I see the rationale for this mod for people with lots of stuff drawing off the house battery constantly. Like some folks here have fridges on all the time, or banks of battery chargers for tools, or full time world travelers that have a lot of auxiliary loads. For situations like this, having a larger capacity battery in the house position makes lots of sense.

Based on how we use our 200, I opted to not do this mod. I kept the larger battery as the starting battery and the smaller one for house loads. I haven’t seen a good rationale for doing this modification in my personal use cases.
 
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I spoke to Christo this morning. He felt the need to call about my email and not just give me a stock answer. That's good service. We discussed lots of options and ideas, but the gist of whole battery situation was Keep It Simple. Here's a bullet point list:
  • Unless you're going off-grid for many many days at a time, there's no reason for a triple battery setup.
  • Lithium is great for power hungry applications, but there are limitations with heat and cold that can damage the battery, or cause it to not charge.
  • He's hardly seen anyone need an inverter as most all devices can be 12V charged.
  • There is little reason to move the starter battery over to the AUX position. Christo even said that he was having difficulty finding a Lead Acid Group 35 starter battery that would fit in their tray. This introduces too many issues and extra work.
  • If you need to jump yourself, you can do so with an AGM battery using a switch under the hood. There's no need for fancy wiring or solenoids (that just adds another failure point). You'll not want to leave this switched on all the time and is a rare situation where AGM to Lead Acid hookup is fine since it's so short of a time. Lithium, not so much due to current draw being too much for the BMS to handle.
  • Use a dual battery system but don't mount solar panels on the roof rack. This will mean you need to park in the sun, and that can get uncomfortable. Get fold up, rigid solar panels with a lead to plug into a BCDC Charger (they recommend the RedArc BCDC50D).
  • Wire your winch, driving lights, compressor to the starter battery. Make sure the engine is running when using these devices.
  • House draws (chargers, camping lights, fridge, etc) should stay on the House battery.
  • Run main power lead from House Battery to the back to a distribution block (if you have a drawer system to mount the block to).
  • With your Dual Battery System, run your power through a hole in the firewall grommet that's just big enough to fit the wire through. That should be water proof enough. If you want more water proofing, use urethane sealant (what our friend's "Down Under" call "Sikaflex").
This was a ton of great info. I know that personally, I get way too "in my head" about projects (my wife hates that) and I need a reality check. I want to do this electric work myself as a fun project. But we all know that it can get dangerous fast if you don't do this correctly. Christo gave me the names of the products they use to wire up a vehicle.

  • Deutsch Connectors
  • PowerWerx
  • Waytek Cable
  • Hyrdalic or heavy duty ratcheting crimper
  • Cable sleaving even though the power cables have good insulation
  • High Quality ring terminals
  • Heat Shrink
With everything that was discussed, I'm rethinking what my next step needs to be. I should probably place orders for items I'll need that are hard to come by (trays, etc) and stock pile that. I think I need to get my rear drawer system in order next. I need a place to mount that distribution block. Once I have that, do I go AGM in the Group 35 AUX tray or do I go Lithium in the back (way overkill for my power needs)? Obviously the heat/cold is an issue and I know BattleBorn has a new battery out that can heat itself. But it would be nice to jump the vehicle from the House battery. I do have a super capacitor jump pack arriving tomorrow. If the Starter battery was so dead that it couldn't provide enough power to the capacitor, I could theoretically use the Lithium to charge the pack at it's desired discharge rate (depending on BMS in the battery) and move the pack to the Starter battery terminals. See! I'm getting too into my head again...
 
Another way to keep your system simple is to forget about dual batteries and carry a jump pack.

Slightly more work, but also pretty straightforward is a dual battery setup with jumper cables for the rare occasion you need to self-jump.

Even the self jump via solenoid is pretty straightforward, especially if you have a switching system already in place (Switch-Pros or SPod for example), but even if you don’t, you can throw in a simple switch.
 
I'm planning on getting a Slee second battery tray, install an AGM battery in the secondary position, and install another Perfect Switch Dual Rectifier. I've run the DR on my 100-series for years and it works beautifully with no active management needed, and it sends high current to exactly where it's needed based on battery health and load. I haven't made any changes to my '21 200-series yet, but this will be on the list....it's nice having a second battery for self-jumping (haven't needed that yet) and for worry-free powering of aftermarket loads.
 
I’ve got something similar to that rectifier for the two lead acid deep cycle batteries (one for starting, one for the trolling motor) on my little aluminum boat. It came to me that way, and it seems to work fine. I run AGM batteries on my 200, so have been using a Redarc BCDC.
 
I agree with KISS. Backup and re-assess your motives. I think most of us want more power reserves. And more capability. Maximizing reserve, expanding capability, while managing complexity and cost.

Somewhat a misnomer, but traditional dual batt setups only partially answers those questions above. Devices are either connected to the starter or house battery, providing still a single battery worth of power, in reserve or ampacity support. Sure, there's more capacity overall, but not for each device. What the traditional dual batt setup really solves is a separation of concerns. And maybe self jumping if it's wired for that.

If added capability is the question, in the form of supporting a large inverter with the engine off, the practical way is lithium as it's the only chemistry that really can support the demanding current rates. AGMs while having better discharge capability than FLA, still only goes so far. Lithium's don't like engine heat (nor to AGMs really). So if one is locating the battery in the rear, might as well go towards an integrated portable solar generator type setup. It's a beautiful thing to run blenders, coffee makes, blow dryer, practically whatever you can plug into a wall at home.

In my mind, the real KISS to dual batts underhood, is setting them up as a single bank. This removes the complexity of handling multiple banks and charging issues. Wired this way, they truly give "dual batt" performance in reserve and ampacity support - giving even FLAs a chance of supporting high power inverters for example. It'll charge faster too, as fast as the alternator can charge (no need for DC-DC charger complexity or bottlenecks). While it doesn't answer the separation of concerns, the reality is that true dual battery reserves makes it that much harder to drain. Adding a low voltage cutoff protects the battery system further. And a portable lithium jumper is the ultimate backup as it's a truly separate device that isn't subject to potential cascading failure modes.

 
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