Run a 12V fridge on your stock starting battery once and you’ll understand why this matters. You’ll wake up to a warm cooler and a truck that won’t start — two problems at once. A proper off-grid power system fixes that permanently, but the options are genuinely confusing if you haven’t done this before. Here’s exactly how to think through it.
Start With Your Actual Load
Before you buy anything, figure out what you’re actually running. Most overland rigs have some combination of a 12V fridge (30–65 watts), interior lighting (5–15 watts), phone and device charging (10–30 watts), and occasionally a small inverter for 120V items. A 45L fridge running a typical compressor cycle in moderate temps draws roughly 2–3 amps per hour on average — about 50–70 amp-hours per day. Everything else is noise compared to the fridge.
If you’re running one fridge and basic lighting on a two- or three-day trip, you need to offset roughly 70–100Ah per day. That number drives every other decision.
Battery Bank: AGM vs Lithium
This debate swallows more forum threads than almost anything else. The short version: lithium wins on every technical metric, but AGM is still reasonable if you’re watching the budget closely.
AGM (Absorbed Glass Mat): Cheaper upfront — a 100Ah AGM runs $150–$200. Heavier at 60–70 lbs for 100Ah. And here’s the critical thing most people miss: you can only use about 50% of rated capacity before you risk damaging it. A “100Ah” AGM is really a 50Ah usable battery.
Lithium (LiFePO4): $250–$500 for 100Ah — Battle Born, Renogy, Dakota Lithium, and AIMS are all in this range. Lighter at 25–30 lbs for 100Ah. You can actually use 80–90% of rated capacity. They charge faster and handle partial states of charge better than AGM. For overlanding, lithium is almost always the right call. You’re not running this in a stationary application for 10 years — you’re loading it, moving it, and running it hard on trips.
How Much Battery Do You Actually Need
For a single-fridge rig doing 2–3 day trips, 100Ah lithium is the floor and 200Ah is comfortable. Here’s the math: 100Ah lithium gives you 80–90Ah usable. One fridge at 60Ah per day gets you roughly 1.3 days without any charging input. That sounds tight — and it is, without another charging source. Add solar or a DC-DC charger and 100Ah handles 2–3 day trips without stress.
200Ah lithium gives you 160–180Ah usable. Two fridges, extra lighting, heavy cloud cover blocking your solar — 200Ah handles all of it. If you’re doing longer trips or running a bigger setup, start at 200Ah and don’t look back.
DC-DC Charging: More Important Than Solar
Most people think about solar first. The thing that actually keeps your battery topped off is your alternator — but you can’t wire your aux battery directly to your starting battery or you risk draining both. A DC-DC charger (also called a battery-to-battery or B2B charger) solves this. It takes alternator voltage and steps it up to properly charge a lithium bank, protecting both batteries in the process.
The Renogy 40A DC-DC charger runs about $120 and handles most single-battery setups fine. REDARC’s BCDC1225D at around $280 is the higher-end option, and it has a built-in solar input so you don’t need a separate charge controller — one unit handles both. If you’re building this system once, the REDARC dual-input unit is the move.
On a typical four-hour drive day, a 40A DC-DC charger puts 120–160Ah back into your battery. That drive alone keeps most builds self-sufficient — solar is the backup, not the primary.
Solar: Real-World Numbers
A 200W solar panel in full sun produces about 10–12 amps per hour. Six hours of solid sun is optimistic in most real environments — figure 50–70Ah on a good solar day, 25–40Ah when it’s overcast. That’s meaningful as a supplement. Most builders land on 100–200W of panel capacity.
Renogy and Rich Solar are the standard picks at $100–$200 for 100W panels. Rigid panels consistently outperform flexible ones — flexible panels trap heat underneath, which cuts efficiency, and they have a shorter lifespan. If you have a roof rack, bolt-mount a rigid panel. For the charge controller, if you’re not using the REDARC combo unit, a Renogy Wanderer 30A PWM controller handles up to 400W of panel for $25. Step up to a Renogy Rover 40A MPPT (~$80) if you want better efficiency when sun is low.
Inverter: Probably Not Right Away
An inverter lets you run 120V devices — laptop chargers, camera batteries, the occasional power tool. Most overlanders discover they don’t actually need one as often as they thought. A 12V car charger handles laptops, USB-C handles everything else, and camp cooking runs on propane. If you do want one, a 300–500W pure sine unit (Renogy or Giandel, $40–$70) covers the occasional need without heavy system overhead. A 2,000W inverter is almost certainly overkill unless you’re running a specific tool that demands it.
The Setup Most Builders Land On
After all the forum threads, all the YouTube rabbit holes, the setup most single-fridge overland builds actually settle on looks like this: one 100Ah lithium battery, a REDARC BCDC1225D for combined alternator and solar charging, one 100W rigid panel, and a 300W inverter if needed. Total cost: roughly $700–$900 depending on the lithium brand. It’s not the cheapest path, but it’s the system you build once and never think about again — which is exactly what you want when you’re three hours from the nearest town.
If you’re tracking your build parts, logging prices, and comparing options across sources, Build List Garage makes it easy to organize your full parts list and share your rig setup with one link. Download it free from the App Store.