I'm shopping for a new fifth wheel and noticed that most of the models I'm looking at come equipped with 12V refrigerators instead of the propane fridges I've had in my previous travel trailers. Over the years with my other RVs, I've always been confident that the house batteries would charge while driving since they're connected to the tow vehicle's charging system through the umbilical cord.
However, I keep reading concerning posts online about 12V refrigerators not staying cold during travel days because they supposedly drain the house batteries faster than the tow vehicle can charge them. This has me puzzled because I've never had charging issues while towing before. If the 12V fridge is running off the same house battery system that gets charged by my truck while driving, shouldn't the charging system be able to keep up with the fridge's power demands?
I'm trying to understand the actual power requirements of these 12V fridges and whether my tow vehicle's charging system through the 7-way connector will realistically be able to maintain the batteries and keep the fridge running properly during long travel days. What kind of amperage draw should I expect from a typical RV 12V refrigerator, and how can I verify that my charging system is working adequately while towing?
12V fridges draw 3-6 amps and your tow vehicle should provide enough charging through 7-way connector. Check voltage at trailer while towing - should see 13.5V+ if charging properly.
You're absolutely right to be confused about this issue! The problem isn't that your batteries won't charge while driving - they should still charge just like in your previous travel trailers. The real issue is that 12V refrigerators are massive power hogs that can consume 4-8 amps when running, averaging 2.5-4.5 amps with cycling, which often exceeds what your truck's alternator can provide to the trailer batteries through the 7-pin connector. Your truck typically only sends 8-10 amps maximum to the trailer, and after accounting for other 12V loads (lights, fans, water pump), there often isn't enough power left to keep a hungry 12V fridge running effectively. This creates a net drain on your batteries even while driving, causing the fridge to warm up during travel days.
The solution isn't avoiding 12V fridges entirely, but rather understanding their power requirements and potentially upgrading your charging system to handle the increased demand. Many RVers successfully run 12V fridges while traveling by installing higher-output charging systems, additional battery capacity, or supplemental charging methods like solar panels.
The fundamental issue is a mismatch between power consumption and charging capacity. Traditional RV appliances like propane fridges, LED lights, and water pumps use relatively little 12V power - maybe 2-3 amps total. Your truck's alternator could easily keep up with these modest demands through the standard 7-pin trailer connector, which typically provides 8-10 amps maximum charging current to your trailer batteries.
Modern 12V refrigerators, however, are essentially large coolers with compressors that cycle on and off. When running, they can draw anywhere from 4-8 amps continuously, with some larger models pulling even more. A typical 12 cubic foot 12V fridge might average 2.5-4.5 amps over a 24-hour period, but during hot weather or when the fridge is working hard to cool down, it could run almost continuously at 7-8 amps.
The charging wire in your 7-pin connector is typically 12 AWG, which limits current flow due to voltage drop over the length of wire from your truck's alternator to your trailer batteries. By the time power travels through your truck's wiring, the 7-pin connector, and your trailer's charging wire, you might only see 13.2-13.8 volts at the batteries instead of the 14+ volts needed for optimal charging. This reduced voltage significantly impacts charging efficiency.
Additionally, your truck's alternator is primarily designed to maintain your truck's battery and run your truck's electrical systems. The "extra" power available for trailer charging varies significantly based on your truck's electrical load, engine RPM, and alternator capacity. During idle or low RPM situations, there may be very little excess charging capacity available.
Before assuming you need major modifications, test your current charging system's actual performance. You'll need a digital multimeter and an amp clamp meter to measure both voltage and current flow. With your truck running and connected to a trailer (or a test setup), measure the voltage at your trailer's battery terminals - you should see 13.5-13.8 volts for acceptable charging. If you're seeing less than 13.5 volts, you have a charging system problem that needs addressing regardless of fridge type.
Research the specific power consumption of any 12V fridge you're considering. Manufacturers should provide amp draw specifications, but real-world consumption can vary significantly based on ambient temperature, insulation quality, and usage patterns. A fridge rated at 3.5 amps might actually draw 6+ amps in hot weather when cycling frequently. Factor in other 12V loads in your fifth wheel - slide motors, fans, lights, and electronics all consume power that reduces what's available for the fridge.
Consider your typical travel patterns and camping style. If you primarily stay in RV parks with hookups, the 12V fridge's travel performance matters less since you'll be on shore power most of the time. However, if you frequently boondock or take long travel days, the fridge's ability to maintain temperature while driving becomes critical. Some RVers find that pre-cooling their fridge on shore power, then adding frozen gel packs or ice blocks, helps maintain temperature during travel days when the 12V system struggles.
Evaluate your trailer's battery capacity and age. Older batteries lose capacity and charging efficiency, making the power balance problem worse. If your batteries are more than 3-4 years old or showing signs of sulfation, replacing them might be necessary regardless of your fridge choice. Consider upgrading to higher-capacity batteries or adding a second battery bank if space and weight allow.
The most effective solution is upgrading your trailer's charging system to handle the increased power demands. Start by installing a DC-to-DC charging system, such as a Victron Orion or REDARC BCDC unit. These systems boost the voltage from your truck's 7-pin connector and provide regulated 14.4-volt charging regardless of engine RPM or electrical load. A 40-amp DC-to-DC charger can provide sufficient power to run most 12V fridges while maintaining battery charge, though you may need to run dedicated 10-gauge wire from your truck's alternator to maximize charging current.
For a comprehensive solution, consider installing a battery isolator and higher-capacity alternator in your truck. This involves connecting your trailer batteries directly to your truck's charging system through heavy-gauge wire (6-8 AWG) and an automatic isolator that prevents your truck battery from being drained when parked. This setup can provide 30-50 amps of charging current, easily handling any 12V fridge plus other electrical loads. Installation requires running new wire from the engine compartment to your hitch, but the performance improvement is dramatic.
Supplement your charging with solar panels if your fifth wheel has adequate roof space. A 400-600 watt solar system with an MPPT charge controller can provide significant charging current during sunny travel days, reducing the load on your truck's charging system. Solar is particularly effective for maintaining batteries during stops or when parked, allowing your truck's alternator to focus on running the fridge while driving. Modern solar installations can be integrated with DC-to-DC charging systems for maximum efficiency.
Consider upgrading to lithium batteries if your budget allows. Lithium batteries charge more efficiently, accept higher charging currents, and maintain voltage better under load compared to traditional lead-acid batteries. A lithium battery bank can provide steady power to your 12V fridge even when charging input is marginal, and they recharge much faster when adequate charging current is available. The higher upfront cost is often justified by improved performance and longer lifespan.
Electrical system modifications involving your truck's alternator and charging circuits should be performed by qualified automotive or RV technicians. Installing battery isolators, upgrading alternators, or running heavy-gauge charging wire requires knowledge of automotive electrical systems and proper connection techniques. Improper installation can damage your truck's electrical system or create safety hazards. Many truck accessory shops specialize in auxiliary charging systems for trailers and can design a system appropriate for your specific truck and trailer combination.
If you're not comfortable working with 12V electrical systems, have a certified RV technician evaluate your trailer's current charging system and recommend appropriate upgrades. They can perform comprehensive electrical system analysis and ensure all modifications meet safety standards.rm load testing on your batteries, measure actual charging performance, and recommend appropriate solutions for your specific setup.re actual charging current from your truck, and calculate the power requirements for your specific 12V fridge model. Professional installation ensures proper wire sizing, fusing, and connection techniques that maximize system reliability and safety.
Consider consulting with solar installation specialists if you're planning a comprehensive power system upgrade. Many RV solar companies now offer integrated solutions that combine solar charging, DC-to-DC charging, and battery management systems. These professionally designed systems can optimize charging from multiple sources and provide the monitoring capabilities needed to understand your power consumption patterns and system performance.
Help us improve this article by flagging technical issues or inaccuracies.
Was this guide helpful?
Try our free RV calculators and tools to help diagnose and plan your repairs.
Browse RV ToolsWeight calculator, electrical planner, propane estimator & more