Dual Battery + Solar for Weekend Overland Trips

The whole point of overlanding is being self-sufficient — but the moment you camp two nights with a fridge and a few lights, you'll discover that the truck's starter battery isn't built for it. Lead-acid starter batteries deliver enormous current for short bursts (cranking), not sustained energy over hours. Run one down to 50% on a fridge overnight and you'll cut its life in half. The solution is a dedicated house battery, ideally with solar input.

The three numbers you need

• • Daily watt-hours consumed (fridge ~30Wh per hour run-time, LED lights ~20Wh per night, USB charging ~30Wh, etc.)
• • Battery bank capacity in Ah at the system voltage — AND the usable depth-of-discharge for the chemistry
• • Solar wattage + average peak sun hours in your area (4–5 hours is typical for the US southwest, 3–4 for the northeast)

Depth of discharge by chemistry

Not all Ah are equal. A 100Ah AGM gives you ~50Ah usable before life-span drops sharply. A 100Ah LiFePO4 gives you ~90Ah usable, weighs about a third as much, and tolerates 4,000+ cycles vs the AGM's 500–800. Lithium costs 3–4× more up front but the per-cycle cost over a decade is lower.

• • Flooded lead-acid → 35% usable, ~300 cycles
• • AGM (standard) → 50% usable, ~500 cycles
• • AGM (spec / EFB) → 60% usable, ~800 cycles
• • LiFePO4 → 90% usable, 4,000+ cycles, ~1/3 the weight

Sizing solar for daily replenishment

A 100W panel in good sun produces roughly 75W average over 5 hours = 375Wh per day. A typical overland fridge + camp lighting + USB charging draw is ~400–600Wh per day. So 100W panels are the bare minimum; 200W gives you a buffer for cloudy days; 400W means you barely think about it. The Solar & Dual Battery calculator tells you exactly how many days of autonomy you have given consumption + battery + solar inputs.

Where to mount the lithium pack

LiFePO4 hates charging below freezing — the cells will degrade if charged at temperatures below ~0°C. If you're camping in winter, mount the bank in a heated location (engine bay or in-cabin) or buy a pack with internal cell heaters. For 9 months of the year in the lower 48, under-bed or rear-cargo mounting is fine.

The classic camping load list

• • ARB or National Luna fridge (50L) — ~30Wh/hr running, ~50% duty cycle → ~360Wh/day
• • LED dome lights × 4, 2 hours/night → ~80Wh/day
• • Phone + tablet charging — ~50Wh/day
• • Diesel heater (winter) — ~120Wh/night including startup
• • Total budget for a typical setup: 500–600Wh/day