How the check works

Fridges are the big number. A 40–50 L camping fridge uses roughly 360 Wh per day; a 60 L+ or dual-zone fridge uses around 540 Wh per day. Tick the hot-weather option and we bump those by 50% — fridges work noticeably harder above 35°C.

Camp lights are 10 W per hour. Starlink draws about 18 W on average. A 12V fan or small accessory is roughly 10 W. Phones, tablets and cameras together come to about 80 Wh per day; laptops about 60 Wh; a set of drone batteries about 90 Wh.

For 220V appliances through an inverter we use (watts × minutes ÷ 60) and then divide by 0.85 to account for inverter conversion losses. That's why a 1,000 W kettle for 6 minutes a day works out closer to 120 Wh than 100 Wh.

Battery capacity on the sticker isn't the same as usable capacity. We treat:

• Lead-acid / AGM as 50% usable — going deeper kills the battery quickly.
• Lithium as 80% usable — conservative compared to the 90–95% some manufacturers claim, to leave headroom for cold mornings and battery age.
• Portable power stations at 85% of their rated Wh — accounting for inverter and conversion losses on the way out.
• Your starter battery on its own as 0 usable — draining it will leave you stranded, not just inconvenienced.

Driving recharges through a DC-DC charger. We assume a 25 Acharger at 13.2 V with 85% efficiency, which works out to about 420 Wh for 1–2 hours of driving and 840 Wh for 3+ hours. For portable power stations charging off a 12V socket at ~8 A, it's much slower — closer to 130 Wh or 260 Wh for the same driving times.

Solar is calculated on 4 effective sun-hours per day at 70%real-world efficiency: a 100 W panel returns about 280 Wh per day, a 200 W panel about 560 Wh per day. South African sun is good, but shade, cloud, panel angle and dust all eat into that — the derating is there for a reason.

Recharge never overfills the battery. If your panels and alternator put back more than you used, the extra is wasted, not banked.

We start the trip with a full battery, then for each day we subtract the daily demand and add the daily recharge, capped at full. The first day your balance drops below zero is the day you go dark. If that never happens across the trip, your setup passes.

Day colours on the chart: green above 40% remaining, amber between 10–40%, red below 10% or failed.

We've kept the maths conservative on purpose. Real-world results vary with heat, battery age and wiring. A check that tells you "you'll be fine" only to leave you with a warm fridge on day three is worse than no check at all.

If you want a recommendation specific to your vehicle, your wiring and your trips, that's what your nearest Opposite Lock fitment centre is for. Bring the result with you.