Where to Mount Your LiFePO4: Inside vs Outside the Van

The trade-off is space and ventilation. LiFePO4 batteries don't off-gas during normal operation (unlike lead-acid), so ventilation isn't strictly required. But a thermal runaway event — extremely rare but not impossible with a faulty BMS — would release toxic fumes. Most builders compromise: mount inside in a semi-sealed box with a small vent to the outside. This gives you temperature control and safety ventilation. Popular mounting spots: under the rear bench (most common), behind the driver seat, in a custom box under the bed platform. Avoid mounting directly on the metal floor without insulation — the cold floor wicks heat from the battery overnight. A 20mm foam pad underneath makes a real difference.

Indoor Mounting: Maximizing Battery Performance#

LiFePO4 batteries perform best between 15°C and 35°C (59-95°F). Below 0°C, most BMS units cut off charging entirely to prevent lithium plating — your solar and DC-DC charger become useless until the battery warms up. This is the strongest argument for indoor mounting. Inside the van, ambient temperature rarely drops below 5°C even in winter if you're running a diesel heater. My battery sits under the rear bench in a plywood box lined with 10mm closed-cell foam on all sides. The foam serves double duty: thermal insulation and vibration dampening. I added a small 12V pad heater ($25, 15W) controlled by a thermostat that kicks on at 5°C — this keeps the battery chargeable even during cold nights. Total additional cost: about $40. The performance gain in winter is dramatic — without it, I'd lose 3-4 hours of morning charging time waiting for the battery to warm up naturally.

Outdoor/Underslung Mounting: When It Makes Sense#

Some builders mount batteries underneath the van in a sealed metal box, similar to how manufacturers mount factory auxiliary batteries. This frees up interior space — a real advantage in smaller vans like the VW Transporter or Renault Trafic. The box needs to be IP65 rated minimum (sealed against water jets and dust). Weld or bolt a steel enclosure to the chassis rail, line it with closed-cell foam, and add drainage holes at the lowest point in case water does get in. The downsides are real though: exposure to road spray, rocks, temperature extremes, and difficult access for maintenance. In cold climates (anywhere that regularly drops below -5°C), underslung mounting means your battery will refuse to charge on winter mornings. I've seen builds in Scandinavia where the underslung battery was essentially dead weight from November through February. If you're a summer-only traveler in mild climates, underslung works. For full-time vanlife in variable climates, mount inside.

Mounting Hardware and Safety Details#

However you mount, secure the battery for a crash scenario. A 25kg LiFePO4 at 50 km/h impact becomes a 750kg projectile. I use M8 threaded rod through the battery box base, bolted to the van floor with large fender washers and Nyloc nuts. The battery sits on anti-vibration pads inside the box and is strapped down with a ratchet strap rated for 500kg. Always mount the battery with terminals facing a direction where a tool can't accidentally bridge positive to negative — a dropped wrench across exposed terminals creates a dead short capable of 500+ amps. Cover terminals with rubber boots after connecting cables. And keep a Class D fire extinguisher within arm's reach — lithium fires won't respond to a standard ABC extinguisher. These cost $40-60 and they're a non-negotiable safety item in any van with lithium batteries.