Camping Mode Battery Isolator

Camping  Mode - Battery Isolator

Thanks to Kris Eric for doing the hard investigations and writing up the below option to isolate your batteries while camping. This Mod is useful for people having issues with their batteries going flat when vehicle is used at rest (for instance if you camp with using a rooftop tent).

 DISCLAIMER: This post describes electrical modifications to a vehicle, shared for information only.

Working on vehicle electrical systems carries real risks — fault codes, damage to electronics, warranty implications, fire risk if done poorly, and a dead alternator if operated incorrectly.

If you're not confident with crimping heavy cable and working around a cranking circuit, have an auto sparky do the install. Follow at your own risk. Your vehicle, your responsibility.

 SOLVED: GRENADIER FLAT START BATTERY WHEN CAMPING — FULL DIAGNOSIS + FIX

Like a few others here, I kept killing my start battery on multi-day camps. Battery down to 11.7V, no start, multiple times. Single start battery, house battery on DCDC, 90W solar panel — and still flat after 2 days at camp. Here's what I found with a DC clamp meter on the negative terminal, and what I did about it.

 THE MEASUREMENTS (this is the interesting bit)

• Engine off, vehicle awake: 6-7A draw

• Screens go dark after 5 min: drops to ~2A

• True sleep (relay click ~2-5 min after wake events): 0.6A

• That's ~14Ah/day BEFORE any door openings

• Every door open/close wakes the whole system: 6.5A for ~3 minutes, then it has to sleep all over again

• With all aftermarket gear disconnected (just factory systems): still 0.6A — so it's the vehicle, not accessories

• Pulling the two BCM (Body Control Module - controls doors and access switches) fuses (FC05 40A + FC06 30A, dash fuse box): drops to 0.4A

Healthy sleep current on a modern vehicle should be 30–80mA. The Grenadier sits at ~600mA asleep, and camping door-cycles stack wake events on top. A 90W panel can't win that fight. That's why our batteries die at camp and not in the driveway.

 THE FIX I CHOSE: MASTER ISOLATOR ON THE NEGATIVE CABLE

After testing the BCM-fuse route (works, but fiddly and still leaves 0.4A), I went with a battery switch in the negative cable = 0A when off. Key detail for the Grenadier:

 The switch must go DOWNSTREAM of the IBS (the battery sensor clamped on the negative post). Never between the post and the sensor, and never run any load direct to the post bypassing it — the smart alternator relies on the IBS seeing ALL current, or it will under-charge your battery and create a new drain problem.

The install (fully reversible, one bolt to undo):

1. Unbolt the factory negative cable at the CHASSIS end (don't touch the battery post, IBS clamp, or its small wires)

2. Factory cable → switch stud A (I drilled the factory lug 8→10mm with a step bit — clean, snug, still fits back on the 8mm chassis stud with a washer)

3. New short cable (I used 20cm of 0 B&S / ~50mm² fine-strand battery cable) → switch stud B → back to the same factory chassis stud, new M8 lug. Cable is larger than the factory cable.

4. Switch surface-mounted on a panel. This is the cranking path — hex-crimped lugs, adhesive heat shrink, no shortcuts.

 PARTS

• Blue Sea 9003e battery switch — 350A continuous, 600A intermittent, 2000A/10s cranking, IP66 (ordered from an AU marine supplier, ~$75.

• 0 B&S marine/battery cable (I had 40cm in the shed — marking "B&S 0 612/0.32 V90" = genuine 49mm² fine-strand)

• 50mm² copper lugs (M10 for switch, M8 for chassis), adhesive heat shrink, split conduit

• Tools: hex lug crimper (hire one), step drill bit, holesaw for the panel

 OPERATION — THIS PART MATTERS

• At camp: park, let the vehicle FULLY sleep first (everything dark, listen for the relay click — 15–20 min), THEN switch OFF.

Cutting power before full sleep is how people get airbag faults that need a dealer reset. After sleep = clean disconnect, same as the documented battery-disconnect procedure.

• Departure: switch ON before opening any door, let it boot (~2 min), start as normal.

•  NEVER switch OFF with the engine running — you'll dump the alternator load and can fry electronics. Mount it where it can't be knocked.

• Expect the battery SOC display to read oddly for a day or two after — the IBS relearns. Normal.

 THE PAYOFF (your numbers may vary)

• Before: 0.6A + door wakes ≈ flat battery in ~2 days

• After, switch off: 0A from the vehicle. My 90W solar now actually gets ahead instead of losing

• Even with NO solar: ~a week+ of camping with zero drain vs 2 days before

Trade-offs while switched off: no alarm, no fob/central locking (lock with the key), no interior lights. Acceptable at camp for me as I run all my roof outlets, fridges and lights from my house battery.

Few pics below of the current draw as well as of the isolator switch and the factory INEOS sticker I relocated from under the seat to next to the switch.

Happy to answer questions in the comments.