How to Convert RV from Lead Acid to Lithium Batteries - Step-by-Step Guide

What's Going On

Converting from your two 6V lead acid deep cycle batteries in series to a pair of 12V LiFePO4 batteries is absolutely doable, but you'll need to upgrade several charging components to properly accommodate lithium chemistry. The main changes you'll need are a lithium-compatible charger, updated charge controller settings, and potentially a new battery monitor system. Many RV owners have successfully made this conversion and found the weight savings, faster charging, and longer lifespan well worth the effort. Your existing 12V system configuration will remain the same since you're going from 12V (two 6V in series) to 12V (parallel 12V batteries), which simplifies the conversion considerably.

The biggest challenge isn't the battery swap itself—it's ensuring your charging sources can properly charge lithium batteries without damaging them or creating safety issues. LiFePO4 batteries require different voltage parameters and charging profiles compared to your current lead acid setup, and most RV converters from more than a few years ago aren't lithium-ready out of the box.

Why This Happens

Lithium batteries have fundamentally different charging requirements than lead acid batteries. Your current lead acid batteries can handle the standard RV converter's charging profile of around 13.6-14.4 volts for bulk/absorption charging and 13.2 volts for float. However, LiFePO4 batteries typically need charging voltages in the range recommended by the manufacturer (verify exact specifications with your battery manufacturer or dealer) during bulk charging and should not be held at continuous float voltage—they prefer to be disconnected or held at a much lower maintenance voltage.

Additionally, lithium batteries charge much faster than lead acid, which can overwhelm older converters not designed for the higher current draw. They also have built-in Battery Management Systems (BMS) that can disconnect the battery if they detect overvoltage, undervoltage, or overcurrent conditions. If your charger doesn't recognize these disconnections and continues trying to charge, it can create system conflicts or even damage components.

Temperature is another critical factor—LiFePO4 batteries shouldn't be charged below freezing (32°F), while lead acid batteries can handle cold weather charging. This means you may need temperature monitoring and heating systems if you camp in cold weather, or at minimum, a charge controller that can read battery temperature and adjust accordingly.

Getting Ready

SAFETY WARNING: Always disconnect all power sources (shore power, solar, and alternator charging) before performing any battery work. Turn off the main breaker and verify power is off with a multimeter before proceeding.

Before starting this conversion, you'll need to inventory your current charging sources and determine which ones need upgrading. Check your converter/charger model—if it's adjustable or has lithium-specific settings, you might be able to simply reprogram it. Look for models with lithium upgrade options or newer units with lithium modes. If your converter is older or fixed-voltage, plan on replacing it with a lithium-compatible unit (verify the correct part for your model with your dealer).

Examine your solar charge controller if you have solar panels. PWM controllers generally won't work well with lithium, so you'll likely need to upgrade to an MPPT controller with lithium settings. You'll also want to check your alternator charging setup—if you have an isolator or basic battery combiner, consider upgrading to a DC-to-DC charger that can properly charge lithium batteries from your alternator.

Gather the necessary tools: multimeter, wire strippers, crimping tool, heat shrink tubing, and appropriately sized wire (typically 4 AWG or larger for battery connections). You'll also need battery terminal cleaning supplies and dielectric grease. Consider purchasing a battery monitoring system that can properly track lithium battery state of charge, since traditional RV monitors often don't read lithium batteries accurately.

Walking Through the Fix

Start by safely disconnecting your old lead acid batteries—turn off all 12V loads, disconnect shore power and solar, then remove the negative cable first, followed by the positive. Clean all battery terminals and cable ends thoroughly with a wire brush and baking soda solution, then neutralize with clean water and dispose of the solution properly. Install your new LiFePO4 batteries, connecting positive to positive and negative to negative to create a parallel 12V bank. Use properly sized cables—most lithium batteries can handle much higher current than lead acid, so ensure your cables can handle the increased capacity.

Next, update your converter/charger settings. If you have a compatible converter, install the appropriate lithium upgrade kit which changes the charging profile to lithium-appropriate voltages. For other units, check if yours has switches for lithium mode. If you're replacing the converter entirely, install the new lithium-compatible unit following manufacturer wiring diagrams—this typically involves connecting AC input, 12V output to your distribution panel, and the battery sense wire to your battery positive terminal.

Configure your solar charge controller for lithium batteries by setting charging voltages according to manufacturer specifications. Set absorption time to 30-60 minutes rather than the 2-4 hours typical for lead acid. If you're installing a new MPPT controller, size it appropriately for your solar array—lithium batteries can accept much higher charging current, so don't under-size the controller.

Install your battery monitoring system by connecting the shunt to the negative battery terminal and running the communication cable to the monitor display. Program the monitor for lithium battery parameters: capacity in amp-hours, Peukert exponent of 1.05 (vs 1.25 for lead acid), and appropriate voltage settings according to your battery manufacturer's specifications. This step is crucial because lithium batteries maintain steady voltage until nearly depleted, making traditional voltage-based monitoring unreliable.

Beyond DIY Territory

While the basic battery swap and charger updates are well within DIY capability, some aspects of lithium conversion require professional expertise. If your RV has a complex inverter/charger system, the programming and integration may require specialized software and knowledge of advanced settings. Professional RV technicians can ensure these systems are properly configured to work with your lithium batteries' BMS and avoid conflicts that could damage expensive equipment.

Consider professional help if you need to upgrade your alternator charging system, particularly if it requires installing a DC-to-DC charger with engine start/stop integration or modifying your engine compartment wiring. Many alternator charging upgrades also involve tying into ignition circuits or installing temperature sensors, which can be complex and potentially affect your engine's electrical systems if done incorrectly.

If you're planning to add heating elements to your lithium batteries for cold-weather charging, this often requires 12V heating pads, temperature controllers, and additional wiring that should be installed by someone familiar with RV electrical systems. Similarly, if your conversion reveals inadequate wire sizing for the higher current capacity of lithium batteries, having a professional assess and upgrade your main battery cables and fusing ensures safety and optimal performance. The typical cost for professional lithium conversion assistance ranges from $500-1500 depending on complexity, but it's worthwhile for peace of mind on a several-thousand-dollar battery investment./p>