Under-Bonnet vs Tub-Mounted Dual Battery Systems
Engine bay or tub? Space, heat, cable runs, capacity and cost compared, with the right mount for weekenders and big-lap tourers.
Under-Bonnet vs Tub-Mounted Dual Battery: What's Right for Your Build?
A second battery is the heart of any touring build. The fridge runs off it, the Starlink runs off it, the lights and the UHF and the phone chargers all end up leaning on it. Where you put it decides how much space you keep, how hot it gets, how long your cable runs are, and how much the whole job costs.
Most people end up choosing between two spots: the engine bay, or the tub. Both work. Which one is right comes down to how you actually use the vehicle, and this guide goes through it the way we'd talk it through at the counter, with real mounts, real prices and the install videos.
The short answer
Go under the bonnet if your vehicle has a factory second-battery space, your power needs are moderate, and you want to keep the whole tub free. Go tub-mounted if you need more capacity, most of your gear lives in the back, or the engine bay is too hot or too full. Where should you mount a second battery in a Ford Ranger? For most owners the factory-allocated space under the bonnet is the cleanest answer, and the tub is the better one when you're building around a 150Ah lithium setup with a fridge and Starlink in the rear.
What a Dual Battery Kit Actually Includes
People search "dual battery kit" expecting one box. In reality it's a handful of parts that work together, and the mount is only one of them:
- A mount or tray that holds the battery securely. This is what we make, built around each vehicle's factory points.
- The auxiliary battery itself, sized for what you're running.
- A DC-DC charger or isolator so the second battery charges properly from the vehicle without ever flattening your starter battery.
- Fusing and cabling between the batteries, the charger and your accessories.
Whichever spot you pick, the electrical side should be done by a licensed auto electrician or at least checked by one. A mount that bolts in cleanly is only half the job.
Under-Bonnet vs Tub: The Five Things That Matter
1. Space
The engine bay on most modern utes and 4WDs has a spot Ford, Toyota and Volkswagen left for a second battery. Use it and you give up nothing: the tub stays completely free for recovery gear, tools and camp kit. Go tub-mounted and the battery needs a home in the load area, either tucked under the tub where it's hidden, or in the wheel arch area where space is awkward anyway.
2. Heat
This is the biggest argument against the engine bay. Under the bonnet runs hotter than the tub, and batteries don't love heat. The fix is picking a battery whose maker says it's suitable for engine bay use, and checking the maximum operating temperature on its spec sheet rather than assuming. A tub or under-tub battery sits well away from engine heat, which is why owners running larger lithium batteries often prefer it.
3. Cable Runs
Every second battery needs two cable runs: one to charge it from the vehicle, and one to feed your accessories. Under the bonnet, the charging run is short because you're next to the starter battery and the alternator, but the feed to the fridge and gear at the back is long. Tub-mounted flips it: the battery sits right next to the fridge, Starlink and rear accessories, but the charging cable has to travel the full length of the vehicle. Long runs mean voltage drop, so cable size matters. Follow your charger maker's guidance, and don't guess.
4. Capacity
Engine bay trays are limited by what physically fits. Our Ranger and Everest tray takes a maximum battery height of 190mm and a maximum weight of 25kg, and the Super Duty tray carries a battery up to 120Ah. In the tub there's more room to play with: our wheel arch mount is built around a 150Ah lithium battery. If your power needs are big, the tub gives you more headroom.
5. Cost
The mounts themselves are close in price: $299 to $499 under the bonnet depending on vehicle, $175 for the compact under-tub mount, and $550 to $599 for the 150Ah in-tub mounts. The bigger swing is the battery, since a bigger battery costs more, and the cable work, since a long charging run means more cable and more labour.
Side-by-Side Comparison
| Under-bonnet | Tub-mounted | |
|---|---|---|
| Space | Uses factory-allocated space, tub stays free | Uses under-tub or wheel arch space |
| Heat | Higher, battery must suit engine bay use | Lower, away from engine heat |
| Charging cable run | Short | Long, needs correct cable sizing |
| Run to rear accessories | Long | Short |
| Battery size | Limited by tray height and weight (25kg max on our trays) | Room for larger batteries, up to 150Ah on our wheel arch mount |
| Mount price | $299 to $499 | $175 to $599 |
| Best for | Weekenders, work utes, moderate power needs | Big-lap tourers, fridge and Starlink in the rear |
Under-Bonnet Mounts by Vehicle
Every one of these drops into the factory-allocated second-battery space and is fitted without drilling. We make them in Queensland and they're built to take common DC-DC chargers.
Ford Ranger, Everest 2022+ and Volkswagen Amarok 2023+
$499 · 304 stainless steel, powder coated texture black · 25kg maximum weight · maximum battery height 190mm · mounts a Redarc BCDC1225D charger · 4.78/5 from 9 reviews
Our best-selling dual battery mount. It fills the space Ford left for a second battery, and an independent test by 4X4 Australia picked out the charger mounting and easy DIY install as highlights.
Toyota Hilux N80 and Fortuner 2015+
$299 · 304 stainless steel · 25kg maximum weight · built around a Delkor HDC27 100Ah battery, and also takes lithium options up to 190mm high · mounts a BCDC · does not suit the 48V mild-hybrid variant
If you searched "N80 dual battery kit", this is the mount at the centre of it. Pair it with the Battery Mounted Fuse Holder ($99) and you have a tidy, fused power point right at the battery. More N80 gear is in our Hilux N80 range.
Toyota Prado 250
$499 · 3mm powder-coated steel · 25kg maximum battery weight · includes a fuel filter relocation bracket · compatible with our bonnet strut kit and dual pole isolator (sold separately)
Want the whole setup in one go? The Ultimate Dual Battery Kit for the Prado 250 starts from $1,799.
Ford Ranger Super Duty 2025+
$499 · carries a battery up to 120Ah · 25kg maximum weight · fits lithium batteries up to 330mm long x 190mm wide x 200mm high, with the washer bottle's height restriction accounted for in the design
Tub-Mounted Options
The Compact One: Under Tub Lithium Battery Mount
The Under Tub Lithium Battery Mount hides a 50Ah Invicta lithium battery in the dead space under the tub. It's fully out of sight, protected from rain, and fits all Next-Gen Ranger models including the Raptor. A Super Duty version is available too.
$175 · 304 stainless steel, laser cut and CNC folded · uses factory captive nuts and bolt holes, so nothing is drilled · Invicta 12.8V 50Ah battery is 277 x 106 x 222mm and weighs 6kg · a Kings 25A DC-DC charger is compatible
The Big One: 150Ah In-Tub Wheel Arch Lithium Mount
This one turns the wheel arch area of the tub into a proper power zone. It's built around a 150Ah lithium battery and gives the DC-DC charger and fuse hardware a dedicated home, so the whole electrical system sits in one tidy spot near the fridge and Starlink.
- 150Ah In Tub Wheel Arch Lithium Mount, Ranger and Raptor 2022+ or Amarok 2023+: $550
- 150Ah In Tub Wheel Arch Lithium Mount with MOLLE Panel and Pocket Storage, Ranger or Raptor 2022+: $599
Both are rated 5.0/5 by owners. Check each product page for the exact configuration and roller shutter compatibility on your tub.
Smaller Vehicles: Jimny JB74
There's no engine bay option on the Jimny, so the cargo area does the job. We make the Cargo Bay Lithium Battery Mount ($275), the Cargo Bay Auxiliary Battery Mount with Power Panel ($599) and the Cargo Bay Auxiliary Power Box ($150).
Want to see the two approaches compared on the same vehicle family? Our real-world comparison of the Super Duty under-bonnet mount and the Ranger 150Ah in-tub mount shows both setups side by side.
Which One Should You Choose? Recommendations by Use Case
The weekender
A fridge, some lights, a few phone charges, and trips of a couple of nights. Your power needs are modest, so go under the bonnet. It's the cheapest, simplest and cleanest install, it keeps the tub free for the kit you actually carry, and the short charging run means less to go wrong. If the bonnet space is already taken, the compact 50Ah under-tub mount is a neat alternative.
The big-lap tourer
Months on the road, fridge running every day, Starlink, laptops, camp lighting. You'll use a lot more power, so lean towards the tub. The 150Ah in-tub mount gives you the capacity and puts the battery, charger and fusing right where the loads are. Plan the charging cable carefully, add solar if you'll be parked for days, and get the electrical work done properly.
The work ute that tours on weekends
Keep the tub free. Under the bonnet suits this better than anything else, because the tray is just as useful on Monday as it is on Saturday. Moderate power for the weekend, full cargo space for the week.
The remote tourer
If you're days from the next town, capacity and heat both matter. A bigger battery in the tub, away from engine heat, is the safer choice, backed by a second charge source like solar. Our Starlink accessories pair well here, since a satellite connection is a real draw on the battery.
Not sure?
Add up what you'll run each day, work out the capacity you need, then see which mount physically holds a battery that size. If both do, pick the one that keeps your cable runs shortest for the gear you use most. And if you're still stuck, email sales@piratecampco.com.au and tell us your vehicle and what you're powering.
The Rest of the Kit: Charger, Isolator and Fusing
A mount without the right electrical parts is a nice tray with a battery in it. These are the pieces that make it a working dual battery system:
Double Pole Isolator Bracket
$95
(also available as a single pole)
Battery Mounted Fuse Holder
$99
(available for several vehicles)
Always check that a battery's dimensions suit the mount you've chosen before you buy it. The measurements are on each product page. Once the power's sorted, the switch clusters and panels give you somewhere clean to control it all from.
Install Guides
Both styles of install are covered in video, and they're easier than most people expect:
- Under-bonnet install: watch the Ranger and Everest under-bonnet mount install or the Hilux N80 install above. Each product page also carries the video.
- Tub-mounted install: watch the under tub mount install above, or the 150Ah in-tub mount video.
The mounting side is a bolt-in job using factory points. The electrical connections are where a licensed auto electrician earns their money.
Frequently Asked Questions
Is it better to mount a second battery under the bonnet or in the tub?
Neither is better for everyone. Under the bonnet keeps the tub free and the charging cable short, but runs hotter and limits battery size. The tub keeps the battery cooler and close to rear accessories and allows a bigger battery, but needs a longer charging cable.
Where should I mount a second battery in my Ford Ranger?
For most owners, the factory-allocated space under the bonnet is the cleanest spot, using a mount like our Ranger and Everest tray. If you're building around a 150Ah lithium battery with a fridge and Starlink in the rear, the in-tub wheel arch mount is the better fit.
What's the biggest battery I can fit under the bonnet?
It depends on the vehicle. Our Ranger and Everest tray takes a maximum battery height of 190mm and a maximum weight of 25kg. The Super Duty tray carries a battery up to 120Ah.
Does an under-bonnet battery get too hot?
The engine bay runs hotter than the tub, so the battery you choose needs to be rated for it. Check the battery maker's maximum operating temperature and confirm it suits engine bay use before you buy.
Do I need a DC-DC charger or isolator as well as a mount?
Yes. A dual battery system needs a way to charge the second battery safely. Our mounts are designed to work with popular DC-DC chargers and isolators, and we sell a BCDC charger and isolator brackets.
Do these mounts need drilling?
No. They use factory holes, threads or captive nuts. The under tub mount, for example, uses existing factory captive nuts and bolt holes, and can be removed without leaving any marks.
Is there an N80 Hilux dual battery mount?
Yes. The Under Bonnet Auxiliary Battery Mount for the Hilux N80 and Fortuner is $299. It doesn't suit the 48V mild-hybrid variant.
Should I install the electrical side myself?
The mounts bolt in with basic tools, but the wiring, fusing and charger connections should be done or checked by a licensed auto electrician.
Pick the Spot That Solves Your Biggest Problem
If you're constantly fighting for tub space, go under the bonnet where your vehicle and battery allow it. If you're constantly fighting for power and building a bigger touring system, the tub is the smarter move. Neither is automatically better. The right one is the setup that fixes the bigger problem in your build.
Browse every option in our Battery & Isolator collection, see the full Next-Gen Ranger range, or read the Super Duty accessories guide to plan the rest of the build around your power setup.
