VW T6 Kombi: Hidden 12V Leisure Battery Install Under the Passenger Seat

The Problem

The owner inherited a disconnected leisure battery setup under the passenger seat of a VW T6 Kombi and needed to reconnect and properly install it. They also wanted a complete hidden 12V electrical system for a day van build without compromising the interior or requiring seat removal for access.

Solution

1. Choose a Renogy 100Ah Core Mini lithium leisure battery, as its compact dimensions allow it to fit under the passenger seat and it can be mounted on its side per manufacturer guidance.

   • The 200Ah and 300Ah Renogy variants are confirmed too large for under-seat fitment.

2. Specify the core charging and inverting components before fabricating anything, so brackets and cable runs are sized correctly:

   • DC-DC charger: a Renogy 12V DC-DC On-Board Battery Charger sized to your alternator output — a 30A unit suits most T6 charging without overloading the alternator, with the 50A unit reserved for vans confirmed to have a smart/Euro 6 alternator that can sustain it (verify the correct amperage and exact model for your T6 generation and alternator before ordering).
   • Inverter: a pure sine wave 12V inverter sized to your loads — a 1000W continuous (2000W peak) pure sine unit covers typical day-van appliances; step up to 1500–2000W only if you intend to run high-draw kit (verify the wattage and model against your intended loads before ordering).

3. Fabricate custom steel brackets and mount them to the seat base frame using rivnuts installed into existing factory holes.

   • The bracket design should keep the battery, DC-DC charger, and inverter accessible and removable without unbolting the seats.

4. Fabricate a busbar from brass bar stock to consolidate all high-current connections, then design and fit a 3D-printed insulated cover over the exposed brass.

5. Size all high-current cable to the components above and keep runs as short as practical (cable gauges given are a starting point — confirm against your final component ratings and run lengths, and de-rate for length):

   • Leisure battery positive/negative to busbar: 25mm² (approx. 3 AWG) for a system feeding a 1000W inverter.
   • DC-DC charger input (alternator/starter side) and output (leisure side): 16mm² (approx. 6 AWG) for a 50A charger; 10mm² (approx. 8 AWG) is adequate for a 30A charger.
   • Inverter feed from busbar: a 1000W inverter draws roughly 85A continuous at 12V, requiring 25mm² (approx. 3 AWG); a 2000W inverter requires 50mm² (approx. 1/0 AWG). Confirm the inverter manufacturer's specified cable size and fuse before final fitment.

6. Run all wiring through flexible conduit, routing cables from the seat bases up behind the B-pillar trim and across to the non-sliding-door panel so the install stays fully hidden behind factory trim.

7. Build a hidden distribution hub into the non-sliding door card containing a fuse box set into an MDF inspection hatch, a WAGO marshalling rail, USB sockets, a 12V socket, and a battery monitor. Protect every circuit and label the fuse box (ratings are typical — set each fuse to the cable and load it protects):

   • Main battery positive to busbar: a high-current ANL/MEGA fuse mounted within 300mm of the battery positive terminal, rated to the system (e.g. 100A for a 1000W inverter system; 150A+ for a 2000W system) (verify against your inverter and cable rating).
   • DC-DC charger feed: 60A for a 50A charger, 40A for a 30A charger.
   • Inverter feed: fuse to the inverter manufacturer's specification for your wattage.
   • LED lighting circuits: 5A.
   • USB sockets: 10A.
   • 12V socket: 15A.
   • Battery monitor / low-draw electronics: 3A.

8. Wire roof and tailgate LEDs via a relay so they trigger from door-open signals but draw from the leisure battery, then add a parallel manual switch for a camping mode override.

   • Add a soft-start module to the cab lights circuit to match the fade-on behaviour of the OEM front LEDs.

9. Use a relay to interface the van's 12V switch circuit with the inverter's dry-contact remote-on input, with the same relay powering the switch LED indicator.