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Battery Relocation NC Chassis

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What’s there to it??

Interested in relocating your NC’s battery into your boot? I’m going to make this guide extremely simple yet give you everything to do a proper job. Now relocating your battery as an overall idea sounds incredibly simple right? What’s there to mess up? There’s quite a few things you’ll need to do and take into account when relocating your battery from the engine-bay to the rear of your vehicle. Before we start, I’d like to mention there is only one downside when doing this. That’s, your chosen battery will now be taking up space in your boot. If you’re happy that you can live with that, then let’s get started.

Step 1 – Choosing your battery and mounting hardware

Let’s start at the heart of your car’s electrical system, the battery. Whenever mounting a battery outside the engine compartment, it should always be a sealed AGM type battery. Period. Why’s this incredibly important? Two reasons, first let’s say the worst thing happens… Your in a wreck, the vehicle’s upside down. If you were to re-use the original battery you’ll find mounted under the bonnet, you’re quite likely to have hydrochloric acid leaking out everywhere. Terrible situation. The second reason is an AGM dry-cell battery does not need any venting. A regular car battery will have a tube that is used to vent away hydrogen gas as your battery charges. So to avoid both of them issues we use a dry-cell sealed AGM type battery can be mounted in the passenger compartment and can be mounted any orientation, no problem.

What options are on the market then for this? There are many options, entirely dependent on what you want and how you intend to use the car. Names that are popular are Oddessy, Dead-weight batteries, Optima, Yausa. In this part, I thoroughly encourage you to do your research and see what will suit your requirements as a battery. Now, once you’ve decided on a battery, you’ll need to find the appropriate hardware to mount it securely in the boot of your vehicle. You will find enclosures like mine, which is a Motamec standard size battery cage. However, if you intend to use the Oddessy style, say PC680 they and many other companies sell an enclosure suited to that batteries dimensions. Again, this is something for you to decide. But what is not up to you is you need to use grade 8.8 steel bolts M8 at a minimum, in my case I used four M8 bolts to secure it to the boot floor. Now in the event of hard driving or an accident the battery is thoroughly secured and not going to become loose and become a flying projectile.

Step 2 – Cable choice, cable join and fusing

Everything I’m going to mention is suited for the NC chassis. So what cable will you need? What you’ll want is 0AWG or 50mm2 ofc welding-cable. I ordered 5 metres to ensure I had loads of length either end and a bit spare for the ground-lead in the boot. 0AWG or 50mm2 is the ideal size for a road car. There are many ways to wire a racecar, so we won’t go into that, but this setup is the simplest and easiest method. Now you’ve got the cable sorted, you’ll need a 50mm2 through-crimp. This is to connect the single 50mm2 cable to 6mm2 fusebox and 16mm2 starter cable. Now onto the incredibly important bit. What fuse to use? So you’ll want to use a 200 amp MEGA fuse in a MEGA fuse holder. I ended up mounting them to a small block of HDPE on the left side of the boot like see in photos. I’d like to add it is also secured to the boot floor by riv-nuts. To connect your cable to the fuse holder’s two M8 studs, you’ll want to get yourself five 50-8 ring-crimp lugs. It’s safe to say, if you haven’t figured out, you’ll need a crimper that’ll crimp 50mm2 lugs to do both your crimp-lugs and the through-crimp under the bonnet. I picked up a SWA branded one for £50 off Amazon. But you could probably borrow one from a friend, or go halves with your mates. Going back to the 200Amp MEGA fuse, the reason we need to fuse this cable is if worst case scenario and your in an accident and the power-cable shorts to the frame you need a fuse to blow and break that circuit to avoid vehicle fires and all sorts. The fuse simply protects the 50mm2 power-cable on its way into the engine-bay from the boot, it will not protect your 16mm2 starter cable or 6mm2 fusebox cable. Those cannot be fused. But the reason the 200 amp MEGA fuse is perfect for this cable is when you start your car. Your starter engages and you have lots of inrush-current that could be anywhere from 300-400Amp for maybe half a second or so before it drops to say 200amp and then the vehicle has started. The 200Amp MEGA fuse will allow this quick inrush-current for a few seconds before blowing. So it will not blow when you try to start the car. This is because it’s a slow-blow fuse and has a time delay based off the inrush-current and how long it lasts. This is why it’s the perfect candidate for our simple battery relocation, and I strongly recommend it.

Step 3 – Making it look pucker

So you’ll want some plastic copex/conduit to cover the power-cable as it routes through the interior up until your engine-bays OEM wiring grommet. This is just above the interior fusebox, a few inches above. You’ll want some expandable-braid to protect it through the engine-bay.

To re-cap I’ve made a shopping list of thing’s you’ll need for this project below.

  • Your new AGM Battery
  • Your battery enclosure/cage
  • 5 Metres of 50mm2 ofc Welding-cable
  • 5 Metres of Plastic conduit/copex non-split (16.9mm ID)
  • Expandable-braid (12mmm I.D. relaxed)
  • Heatshrink
  • MEGA Fuse holder
  • 200Amp MEGA fuse
  • A crimper that can crimp 50mm2 cable
  • 1x 50mm2 through-crimp
  • 5x 50-8 ring crimp-lug

Links to my exact setup are below.

Battery –
Battery enclosure –
Cable –
Copex –
Expandable-braid –
Heatshrink –
MEGA Fuse holder –
200Amp MEGA Fuse –
Cable Crimper –
Through-crimp –
Ring-crimp lugs –
HPDE sheet –

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Join the discussion

  1. Hello,

    Looking at your boot/trunk mounted battery in your NC, your conversion looks far better than any other solutions from various vendors I have seen here in the States. It even looks more complete than the factory boot/trunk mounted battery locations in other versions of the MX-5 Miata!

    I was wondering if you have additional photos and information (eg, actual routing position of the cable) that shows the installation from the boot/trunk through the passenger compartment, and also the connections in the engine bay. Thanks in advance!

  2. Hello,

    Your boot/trunk conversion for your NC MX-5 looks like one of the best shown on the internet, even rivaling the factory installations in other versions of the MX-5. I am curious, and no doubt other readers are, on how you routed the primary and secondary cables through the passenger compartment, engine compartment, and final connections to the starter and other items in the engine compartment. A description and additional photos in these areas would be really helpful to those of use who wish to replicate your installation. Thanks so much!

    1. Hi,

      I will in the future upload more photos in the engine bay. But put simply a 50mm2 through-crimp connects to the two cables that would go to the battery terminal. Essentially two cables join to one. I penetrated through under the oem wiring grommet.

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