Switching your RV or Van from Lead-Acid to Lithium is the best upgrade you can make, but it comes with a hidden danger: Alternator Burnout. In this systems engineering guide, we explain why low-resistance lithium banks destroy stock alternators, how to size a DC-DC charger, and the wiring upgrades needed to handle the 12V revolution.
The Van Life Power Revolution
For decades, Recreational Vehicles (RVs) and camper vans relied on heavy, inefficient deep-cycle lead-acid batteries. You could only use 50% of their capacity, they took all day to charge, and they died every 2-3 years.
Lithium Iron Phosphate (LiFePO4) changed everything. You get double the usable energy for half the weight, and they last 10 years. However, LiFePO4 is not a "drop-in" replacement for the vehicle's charging system. Treating it like one is the fastest way to smoke your engine's alternator and leave you stranded.
1. The Alternator Problem: Physics of Resistance
Your vehicle's alternator is designed to charge a lead-acid starter battery. Lead-acid batteries have naturally high internal resistance. As they get full, they resist the current, naturally tapering off the load on the alternator.
Lithium is different. It has extremely low internal resistance. It is a "current sponge."
If you connect a depleted 200Ah LiFePO4 bank to a standard 100A alternator, the battery will demand everything the alternator can give—often exceeding 100 Amps.
The Failure Mode: An alternator is air-cooled by its own rotation. At idle (low RPM), the fan spins slowly, but the lithium battery still demands 100A. The alternator windings overheat, the diode rectifier blows, and your engine charging system fails. This is a common and expensive disaster for new van builders.
2. The Solution: DC-DC Battery Chargers
You need a device that sits between the Starter Battery (Alternator) and the House Battery (Lithium) to act as a limiter. This is the DC-DC Charger (e.g., Victron Orion-Tr Smart, Renogy DC-DC).
How it works:
1. Current Limiting: A 30A DC-DC charger will never pull more than ~35-40A from the alternator, regardless of how empty the lithium battery is. This protects the alternator from burning out.
2. Voltage Boosting: Alternators output 13.8V-14.2V. Lithium needs 14.4V-14.6V to fully charge and balance. The DC-DC charger boosts the voltage to the correct profile.
3. Wiring Upgrades: The 12V Current Challenge
In a 48V home system, 2000 Watts is only 41 Amps. In a 12V RV system, 2000 Watts (a microwave or induction cooktop) is 166 Amps.
Managing this massive current requires thick copper.
- Inverter Cables: For a 2000W inverter, you need 2/0 AWG or 4/0 AWG welding cable. Anything thinner will get hot and cause voltage sag, tripping the inverter.
- Fusing: You must use Class T fuses for the main battery bank. ANL fuses are okay for smaller loads, but Class T is required to stop the massive short-circuit current of a lithium bank. (See our Wire Gauge Guide).
4. Shore Power Converter Issues
Your RV likely came with a "Converter/Charger" plugged into the wall. Older units (WFCO, Progressive Dynamics) are hard-coded for lead-acid.
The Issue: They enter "Float" mode at 13.2V or 13.6V too early.
The Result: Your lithium battery will sit at 80% charge and never balance.
The Fix: You must replace the converter's main board with a "Lithium Compatible" version or a dedicated LiFePO4 charger that holds 14.4V until the battery is truly full.
5. The "Drop-In" Myth vs. DIY
You can buy "Drop-In" LiFePO4 batteries (like Battle Born) that look like car batteries.
Pros: Easy form factor. Built-in BMS.
Cons: Expensive. Current limited (usually 100A BMS).
The DIY Advantage: Building your own 12V 280Ah bank using four prismatic cells allows you to install a 200A BMS, giving you enough power to run a microwave or A/C unit, which a single drop-in battery often cannot do. It also allows you to fit the battery into weird spaces, like inside a wheel well box.
6. Temperature: The Cold Reality
RVs are often parked in freezing weather. As discussed in our Float Charging Guide, you cannot charge lithium below 0°C.
Best Practice: Install your battery inside the heated living space, not in an external uninsulated box. If you must mount it externally, you need a battery with internal heating pads or a 12V tank heater pad controlled by a thermostat.
Summary
Converting an RV to lithium is more than just swapping batteries. It is a system-wide re-engineering of the charging architecture. By protecting your alternator with a DC-DC charger, upgrading your cabling for high amperage, and managing the temperature of your bank, you create a mobile power station that allows you to boondock for days without noise, fumes, or anxiety.
