When you live and travel in a small space, a reliable refrigerator can make a surprisingly big difference. We wanted a better setup, but we also wanted to keep it small.
That led us to a Renogy dual-input DC-to-DC charger, a 50Ah LFP battery, and a 100W folding solar suitcase. After using the setup on the road, we learned that choosing the right charger is less about picking the biggest number and more about matching the charger to the battery, alternator, solar input, and wiring.
If you are planning a larger RV power system, this RV solar kit buying guide is a useful place to start.
Why We Added a DC-to-DC Battery Charger
Our vehicle already had an alternator, so it made sense to use some of that energy while driving. The problem was that the small amount of charging available through the existing connection was not enough to reliably recharge an auxiliary battery.
A DC-to-DC charger gives the auxiliary battery a controlled charging source from the vehicle. It also keeps the starting battery and auxiliary battery separate when the vehicle is turned off.
For us, that meant we could drive between campsites and put useful energy back into the battery along the way. When we stayed in one place, the solar panel gave us another way to keep the refrigerator running.
A DC-to-DC charger can be useful if you:
- Drive regularly and want to charge an auxiliary battery while traveling.
- Use a battery to run a 12V refrigerator, lights, fans, or other DC equipment.
- Travel during cloudy weather or in areas with limited sunlight.
- Want to combine alternator charging with solar charging.
How a DC-to-DC Charger Works
While you are driving, the alternator charges the vehicle's starting battery and powers the vehicle's normal electrical systems. A DC-to-DC charger draws power from that electrical system, regulates it, and sends it to the auxiliary battery at a suitable charging voltage.
The basic flow looks like this:
Alternator → Starting Battery → DC-to-DC Charger → Auxiliary Battery → DC Loads
A standard DC-to-DC charger uses the vehicle as its charging source. A dual-input DC-to-DC charger with MPPT can also accept power from solar panels, which is what made the most sense for our setup.
If you are mainly interested in running a refrigerator while driving, you may also find Can I Run My RV Fridge on Battery While Driving? helpful.
Standard and Dual-Input DC-to-DC Chargers
The simplest choice is a standard DC-to-DC charger. It charges the auxiliary battery from the alternator while you drive. This is a good fit if your solar panels already have a separate solar charge controller or if you do not need solar input through the same charger.
A dual-input DC-to-DC charger adds solar input. It can accept power from the alternator, the solar panels, or both, depending on the conditions and the charger settings.
In our case, the dual-input option gave us more flexibility. The alternator did most of the work while we were moving, and the portable solar panel helped when we were parked for several days.
The current Renogy DC-to-DC battery charger collection includes different charging currents, voltage options, and dual-input models. Check the product specifications before choosing a model for your vehicle.
How We Chose the Charger Size
The first thing we checked was not the battery's amp-hour rating. We looked at the battery manufacturer's maximum charging current.
This is important because two batteries with the same amp-hour rating may have different charging limits. Battery chemistry, battery management system settings, and the way the batteries are connected can all make a difference.
If batteries are connected in parallel, their available capacity and charging-current limits may increase together. If batteries are connected in series, the system voltage increases, but the charging-current limit usually remains based on the series string.
We also checked the alternator, the distance between the vehicle and auxiliary battery, and the cable size needed for the installation. A larger charger is not automatically better if the alternator, battery, or wiring cannot support it.
Our practical checklist was:
- Maximum charging current of the auxiliary battery
- Battery-bank voltage
- Alternator capacity and vehicle type
- Solar input, if using a dual-input charger
- Cable length and voltage drop
- Fuse, breaker, and disconnect requirements
The chart above is retained from the original installation as a reference. Charger ratings and product availability can change, so use the current product page and manual for final specifications.
One important lesson: do not rely on the battery management system to make an oversized charger safe. The charger should be selected within the battery manufacturer's recommended charging limits. The BMS is a protection layer, not a substitute for correct system sizing.
Where We Installed the Charger
For a towable setup, the charger can be installed in a protected area near the auxiliary battery or in another suitable electronics compartment. For a van or motorhome, the installation location depends on the available space, cable runs, ventilation, and protection from moisture.
We learned that grounding deserves more attention than it often gets. An apparently convenient grounding point did not provide the reliable charging path we expected. Running a properly sized ground connection back to the appropriate battery connection solved the intermittent charging problem.
Use the cable size, fuse ratings, grounding method, and installation distances specified for your charger. The exact requirements depend on the vehicle and charger model.
For a complete RV solar installation sequence, see this RV solar kit installation guide.
Why the Dual-Input MPPT Charger Worked for Us
The dual-input charger gave us two useful charging options without adding a separate alternator charger and solar controller to this small system.
When we were driving, the alternator provided the main charging source. When we were parked, the portable solar panel could continue charging the auxiliary battery. The exact amount of current available from each source depends on the charger model, solar conditions, vehicle, battery, and settings.
MPPT charging can make better use of the voltage available from a solar panel, but the solar input still needs to stay within the charger's voltage and power limits.
If your system uses a separate solar charge controller, see Solar Charge Controller Sizing and How to Choose One. A dual-input DC-to-DC charger can replace a separate solar controller only when the specific product is designed and rated for that configuration.
Which Renogy DC-to-DC Charger Fits Your System?
Renogy's current DC-to-DC charger range includes alternator-only chargers and dual-input models with MPPT.
| Charger type | Best fit | What to verify |
|---|---|---|
| Standard DC-to-DC charger | Alternator-only charging for an auxiliary battery | Battery voltage, maximum charging current, alternator capacity, and wiring |
| Dual-input DC-to-DC charger with MPPT | Systems that combine alternator and solar charging | Solar input voltage, solar input power, battery profile, current limits, and monitoring compatibility |
| 12V/24V or weather-protected model | Installations that need additional voltage flexibility or environmental protection | Supported battery voltage, enclosure rating, mounting location, and cable requirements |
If we were choosing a charger for a new installation today, we would start with the system rather than the product name.
For alternator-only charging, compare the standard DC-to-DC options in the Renogy charger collection. For a system that combines driving and solar charging, compare the dual-input MPPT models.
We would then check:
- Whether the charger supports the vehicle and alternator type
- Whether the charger supports the auxiliary battery voltage
- Whether the battery's maximum charging current matches the charger output
- Whether the solar input supports the panel voltage and wattage
- Whether the charger has the monitoring or current-limiting features we need
- Whether the enclosure and mounting requirements fit the installation location
Using Current Limiting and Monitoring
Some Renogy dual-input chargers support monitoring and current-limiting functions through compatible Renogy accessories and the Renogy app.
That can be useful if you add another battery later, change the charging source, or need to limit the current for a particular battery bank. The available functions depend on the charger and accessories, so check the current product documentation before planning around them.
Our Installation Experience
We installed the charger in a protected storage area and used appropriately sized wiring between the vehicle, charger, and auxiliary battery. A towable system needs a dependable connection between the tow vehicle and trailer, while a van or motorhome may use a shorter hardwired connection.
The installation was not difficult, but it was vehicle-specific. Cable routing, mounting, grounding, and protection from water and road debris all mattered more than we expected.
We would not treat our installation as a universal wiring diagram. Use the manual for your specific charger and battery, and have permanent vehicle wiring reviewed if you are not comfortable checking cable sizing, fusing, or grounding.
What We Learned From Running a 12V Refrigerator
We used a 30A dual-input charger with a 50Ah LFP auxiliary battery to run a 12V refrigerator in the back of our towing vehicle.
The alternator handled most of the charging while we were on the move. The 100W folding solar panel became useful when we were parked and did not want to start the vehicle just to recharge the battery.
The refrigerator was a small, dedicated load, and that made the system manageable. A refrigerator, lights, and other modest DC loads are very different from running an air conditioner, microwave, or power tools through an inverter.
That is the part we would emphasize most: size the system around the actual loads and the way you travel. A 50Ah battery and a 100W panel worked for our particular setup, but they should not be treated as a universal recommendation.
Final Thoughts
For us, the DC-to-DC charger solved a very practical problem. We could charge the auxiliary battery while driving, use solar when parked, and keep the refrigerator running without carrying bags of ice everywhere.
If you are choosing a charger for your own RV, van, truck, or auxiliary battery, start with the battery's charging limit and the available charging sources. Then check the vehicle, solar input, wiring, and protection requirements.
The biggest lesson from our setup was simple: the right charger is not necessarily the biggest one. It is the one that fits the battery and the way you actually use your vehicle.
Shari Galiardi and David Hutchison began traveling full-time after leaving their careers and home in North Carolina in 2012. They restored a vintage camper, added solar, and continued learning through years of travel, writing, and hands-on projects.
