Planning the electrical system for your camper conversion or RV can feel overwhelming. With so many components to consider - batteries, solar panels, inverters, chargers - where do you even start?

Here's what you'll learn: How to choose between 12V, 24V, and 48V systems, why LiFePO4 batteries are worth the investment, how Ohm's Law actually helps you make practical decisions, how to size your battery bank correctly, and the essential safety components you can't skip. Plus, I'll show you exactly how all these components connect together to create a reliable power system for your mobile adventures.

This guide breaks down everything you need to know about 12V electrical systems in simple terms. By the end, you'll understand how each component works and how they fit into your overall system.

Why 12V Systems for Campers?

Most recreational vehicles use 12V electrical systems because:

Automotive compatibility: Your vehicle already runs on 12V
Safety: Lower voltage means less risk of dangerous electrical shocks
Component availability: Tons of 12V appliances designed for RVs and boats
Efficiency: Many LED lights and DC appliances run efficiently on 12V

12V vs 24V vs 48V -- Choosing the Right System Voltage

The 12V system is the default for most camper and van builds, but it's not the only option. Understanding when higher voltages make sense will help you design a better system -- or confirm that 12V is the right call for your project.

12V systems are the sweet spot for most campers, vans, and smaller boats. Your vehicle's starter battery is 12V, the majority of RV and marine appliances are designed for 12V, and the ecosystem of compatible components is enormous. If your total inverter load stays under about 2000-3000W, 12V is almost certainly the right choice. The wiring is straightforward, replacement parts are easy to find, and you won't need to worry about voltage conversion for most of your loads.

24V systems start making sense when you're building a larger system. The key advantage is that for the same power output, a 24V system draws half the current of a 12V system. Lower current means you can use thinner (and cheaper) wire, and you'll experience less voltage drop over longer cable runs. If you're planning an inverter larger than 3000W, or your cable runs between the battery bank and the inverter are long, 24V is worth considering. The downside? Many common 12V appliances won't work directly, so you'll either need 24V-specific gear or a DC-DC converter to step down to 12V for those devices.

48V systems are mostly relevant for permanent off-grid homes and larger installations. They're very efficient for high-power setups and long wire runs, but the component availability for mobile applications is limited. Unless you're building a large catamaran or a seriously overbuilt expedition truck, 48V is probably overkill.

For the rest of this article, we'll focus on 12V systems since that's what the vast majority of camper and van builders will use.

A Quick Ohm's Law Primer

You don't need to become an electrical engineer, but understanding two simple formulas will help you make smarter decisions about your entire system. These aren't abstract theory -- they're the practical foundation for wire sizing, fuse selection, and battery planning.

Ohm's Law: V = I x R

Voltage (V) equals Current (I) times Resistance (R). In plain terms: the voltage across a wire equals the current flowing through it multiplied by the wire's resistance. This is why wire gauge matters -- thinner wire has higher resistance, which causes more voltage drop and generates heat.

The Power Formula: P = V x I

Power (P, measured in Watts) equals Voltage (V) times Current (I, measured in Amps). This is the formula you'll use most often.

Here's a practical example: your 60W compressor fridge runs on 12V. How much current does it draw?

Rearranging the formula: I = P / V = 60W / 12V = 5 Amps.

That 5A figure matters because it determines what size wire you need to run to the fridge and what size fuse to put in the circuit. Now imagine you have a 2000W inverter running at full load: I = 2000W / 12V = 167 Amps. That's a massive amount of current, and it's exactly why the cables between your battery bank and your inverter need to be thick -- typically 2/0 AWG or larger.

This is also why higher voltage systems are appealing for big loads. That same 2000W inverter on a 24V system would only draw 83 Amps, meaning you could use significantly thinner cables.

Core Components of a 12V System

1. Power Sources

House Batteries Your house battery bank stores electrical energy for when you're not plugged into shore power. We'll cover battery types in detail in the next section.

Solar Panels Solar panels convert sunlight into electricity to charge your batteries. They're perfect for off-grid camping and reduce your reliance on hookups.

Alternator Charging Your vehicle's alternator can charge your house batteries while driving using a DC-DC charger or battery isolator.

Shore Power When available, you can plug into campground electrical hookups to power your system and charge batteries.

2. Power Conversion

Inverters Convert 12V DC power from your batteries into 120V AC power for standard household appliances. Choose between:

Pure sine wave: Clean power for sensitive electronics
Modified sine wave: Cheaper but may cause issues with some devices

DC-DC Chargers Regulate the voltage from your alternator to safely charge your house batteries without overcharging.

3. Power Distribution

Fuse Boxes and Breakers Protect your electrical system from overloads and short circuits. Every circuit should have appropriate protection.

Battery Monitors Track your battery voltage, current, and state of charge so you know how much power you have available.

Battery Types: A Deep Dive

Choosing the right battery is probably the single most important decision in your electrical build. Let's break down the options.

Lead-Acid Batteries

Lead-acid batteries come in three main subtypes, and they're not all created equal:

Flooded lead-acid (FLA) batteries are the cheapest option. They use liquid electrolyte and require periodic maintenance -- you'll need to check and top off the water level every few months. They also produce hydrogen gas while charging, so they need ventilation. These are fine for a budget build, but they're heavy, have a shorter cycle life, and must be mounted upright.

AGM (Absorbent Glass Mat) batteries are sealed and maintenance-free. The electrolyte is absorbed into fiberglass mats between the plates, so they won't spill and can be mounted in any orientation. They handle vibration well (important in a vehicle), charge faster than flooded batteries, and don't produce gas under normal use. AGM is a solid mid-range choice and was the go-to recommendation before lithium became affordable.

Gel batteries use a silicified electrolyte that's in a gel state. They're also sealed and maintenance-free, handle deep discharges reasonably well, and work better in hot climates than AGM. However, they're more sensitive to overcharging and require a charger with a specific gel charging profile. They've largely been eclipsed by AGM and LiFePO4 for most camper applications.

LiFePO4 (Lithium Iron Phosphate)

LiFePO4 batteries have become the standard recommendation for new builds, and for good reason. They cost roughly three times what an equivalent AGM battery costs, but the total cost of ownership is often lower when you factor in their advantages.

Every LiFePO4 battery includes a BMS (Battery Management System), which is essentially a built-in computer that monitors each cell and protects the battery. The BMS prevents overcharging, over-discharging, short circuits, and overheating. It also balances the cells to ensure they age evenly. A good BMS is the reason you can largely "set and forget" a lithium battery system.

One important consideration: LiFePO4 batteries don't like being charged in freezing temperatures. Most BMS units will cut off charging below 0 degrees C (32 degrees F) to prevent damage to the cells. If you camp in cold climates, look for batteries with built-in heating pads, or plan to insulate your battery compartment. Discharging in cold temperatures is fine -- it's only charging that's problematic.

For a much more detailed look at lithium batteries, check out our complete guide to LiFePO4 batteries.

Battery Capacity: Ah vs Wh

Battery capacity is usually listed in Amp-hours (Ah), but this number can be misleading when comparing batteries at different voltages. A 100Ah 12V battery and a 50Ah 24V battery actually store the same amount of energy.

The better comparison metric is Watt-hours (Wh), which accounts for voltage:

Wh = Ah x V

So a 100Ah 12V battery stores 1200Wh, and a 50Ah 24V battery also stores 1200Wh. When you're calculating how long your battery bank will last, Wh is the number you want.

Depth of Discharge

Not all of a battery's rated capacity is actually usable. Depth of discharge (DoD) tells you how much you can safely drain a battery without damaging it.

Lead-acid batteries (all types) should only be discharged to about 50%. So a 100Ah lead-acid battery gives you roughly 50Ah of usable capacity.
LiFePO4 batteries can safely be discharged to 80-90%. That same 100Ah capacity gives you 80-90Ah of usable power.

This is a huge part of why lithium batteries are worth the extra cost. A single 100Ah LiFePO4 battery provides more usable energy than two 100Ah AGM batteries, at a fraction of the weight.

System Architecture: How Everything Connects

Understanding the flow of electricity through your system helps you plan your build and troubleshoot problems. Here's the typical architecture:

Power Sources -> Charge Controller/Charger -> Battery Bank -> Distribution Panel -> Loads

Let's walk through each stage:

Power sources (solar panels, alternator, shore power) generate or supply electricity. Each source connects to the battery bank through its own dedicated charger or controller -- a solar charge controller for solar panels, a DC-DC charger for the alternator, and an AC charger for shore power.
Charge controllers and chargers regulate the incoming power to match what your batteries need. They manage the charging profile (bulk, absorption, float stages) and prevent overcharging. Never connect a power source directly to your batteries without a proper controller.
The battery bank is the central hub of your system. Everything flows through it. The batteries store energy and supply it on demand. A battery monitor or shunt sits between the battery bank and the rest of the system to track state of charge.
A main disconnect switch sits between the battery bank and the distribution panel. This lets you cut all power for maintenance or emergencies. A properly sized fuse should also be installed as close to the battery positive terminal as possible.
The distribution panel (fuse box or breaker panel) splits power into individual circuits, each with its own fuse or breaker. From here, wires run to your various loads -- lights, fridge, water pump, USB outlets, and so on.
Inverters, if you need AC power, typically connect directly to the battery bank (before the DC distribution panel) with their own dedicated fuse, since they draw high current.

Grounding and Safety

Poor grounding is one of the most common causes of electrical problems -- and fires -- in DIY camper builds. This is not an area to cut corners.

Chassis Grounding

In most vehicle-based builds, the vehicle's metal chassis serves as the ground (negative) path. Instead of running a separate negative wire all the way back to the battery for every device, you connect the negative terminal to a grounding point on the chassis. Each device then connects its negative wire to a nearby chassis ground point.

This works well, but only if the chassis ground connections are clean, tight, and corrosion-free. Sand the paint off the chassis at each grounding point, use star washers to bite into the metal, and apply dielectric grease to prevent corrosion. A bad chassis ground connection creates resistance, which causes voltage drop and heat -- exactly what you don't want.

Bus Bars

For a cleaner and more reliable installation, many builders use bus bars for both positive and negative distribution. A bus bar is simply a solid metal bar with multiple connection points. You run one heavy cable from the battery negative to a negative bus bar, then connect all your device ground wires to that bus bar. This gives you a central, accessible point to check all your ground connections.

For a thorough treatment of grounding in mobile systems, read our grounding and bonding guide.

Essential Safety Components

Every system should include:

A main fuse at the battery positive terminal -- this is your last line of defense against a dead short
A battery disconnect switch to kill all power when needed
A shunt (for battery monitoring) installed on the negative side
Individual circuit fuses sized appropriately for each wire gauge and load
A low-voltage cutoff to prevent over-discharging your batteries (especially important for lead-acid)

Wire Sizing Basics

Using the wrong wire gauge is dangerous. Wire that's too thin for the current it carries will overheat, melt its insulation, and potentially start a fire. Wire that's oversized wastes money but is otherwise harmless -- so when in doubt, go one size up.

Wire size depends on two factors: the current the wire will carry, and the length of the wire run (remember, you need to count both the positive and negative wire, so a device mounted 3 meters from the fuse box has a 6-meter total wire run).

Longer runs and higher currents need thicker wire. This is because of voltage drop -- the resistance of the wire causes some voltage to be lost as heat. For a 12V system, you generally want to keep voltage drop under 3% for most circuits and under 1% for critical circuits like battery-to-inverter connections.

For detailed wire sizing tables and calculations, check out our wire gauge sizing guide and fuse sizing article. Or use the wire gauge calculator to get instant results for your specific circuit.

Planning Your System

Before buying components, calculate your power needs:

List all your electrical devices and their power consumption
Estimate daily usage for each device
Calculate total daily power consumption in Watt-hours
Size your battery bank for 2-3 days of usage without recharging (and account for depth of discharge)
Size your charging sources to replenish what you use

Common Beginner Mistakes

Undersized house batteries: Always size larger than your minimum calculation
Mixing battery types: Don't mix lead-acid with lithium or old batteries with new
Inadequate wire sizing: Use proper gauge wire to prevent voltage drop and fire hazards
Poor grounding: A solid ground system is critical for safety and performance
Skipping fuses: Every positive wire leaving the battery bank needs fuse protection
Connecting solar panels directly to batteries: Always use a charge controller

Getting Started with VoltPlan

Ready to design your own 12V electrical system? VoltPlan makes it easy to:

Choose from proven templates for campers, boats, and off-grid setups
Add and connect electrical components with drag-and-drop simplicity
Get automatic wire sizing recommendations
Export your complete electrical diagram

The best part? It's completely free for personal use. No electrical engineering degree required!

Next Steps

Understanding 12V electrical basics is just the beginning. Here are some deeper dives to continue your learning:

Start planning your electrical system today with VoltPlan's free designer tool. Turn your van life dreams into a well-powered reality!

12V Electrical System Basics for Campers and Van Life