Battery Equivalents and Replacements

Renogy 12V 40A DC to DC On-Board Battery Charger

Renogy DCC1212-40 is a 12V 40A DC to DC onboard battery charger intended for charging lead-acid and lithium batteries in RVs, boats, yachts, commercial vehicles, etc.

Basically, the Renogy DCC1212-40 battery charger is connected to the alternator powered by an internal combustion engine and charges the house deep-cycle battery. To keep things as safe as possible, the Renogy DCC1212-40 battery charger comes with various built-in features, including the use of a D+ ignition cable and LC current limit cable.

Published: September 21, 2022.

renogy 40a dc dc onboard battery charger

Renogy DCC1212-40 On-Board Battery Charger Features and Specifications

Renogy DCC1212-40 battery charger features physical dimensions of 10.3 x 6.9 x 2.7 inches (261 x 175 x 68 mm), it weighs ~4 pounds (~1.9 kg) and is intended for charging deep cycle AGM, Gel-Cell, Flooded lead-acid batteries, and lithium batteries.

Renogy 12V 40A DC to DC battery charger comes with over-voltage, over-temperature, reverse polarity protection and isolates the input and output circuits to prevent voltage transmission errors and interferences while charging the house battery.

To protect the starting battery from being discharged while the main engine is not turned on, a D+ ignition cable (ordered separately) can be used - as long as the main engine is turned On, the charger will charge the house battery, and as soon as the main engine is Off, the charger will NOT charge the house battery, preventing the starting battery from being discharged.

In order to protect the house battery from too strong charging current, an LC current limit cable (ordered separately) can be used - basically, it halves the charging current from 40A to 20A.

Alternator Sizing

When onboard DC to DC battery chargers are added to the electric system of boats, yachts, RVs, and similar, as soon as chargers start charging, they increase the load on the alternators, so it is very important to choose the DC chargers according to the alternator current. For example, according to the Renogy:

  • Alternator <160 Amps: 20 Amps DC Charger
  • Alternator 160-180 Amps: 40 Amps DC Charger
  • Alternator >180 Amps (preferably 200+Amps): 60 Amps DC Charger

The stronger the alternator, the better it is regarding the additional load.

When the engine is not idle, alternators generally don't have issues with the load or cooling; however, when the engine is idle, alternators are unable to provide strong enough currents (half on average) and may have issues with cooling since their cooling fans are not spinning fast enough.

Thus, if You notice issues with the alternator, limit the charging current using LC current limiting cable. Also, if the house battery doesn't accept 40 Amps charging current, either limit the charging current to 20 Amps or use Renogy DCC1212-20 (12V 20A) onboard battery charger.

DIP Switches

Renogy DCC1212-40 battery charger features 5 DIP switches for configuring the charger, including the battery chemistry and charging voltages.

Also, the charger supports the use of a temperature sensor (also must be ordered separately), ensuring that the proper charging voltages are used for lead-acid batteries during both warm and cold days.

Of course, a temperature sensor is not used when charging lithium batteries.

dip switches

How to Connect the Renogy DCC1212-40 Battery Charger

With so many options, it is very important to properly connect the Renogy DCC1212-40 battery charger to the electrical installations of your RV, boat, yacht, or similar vehicle/vessel.

When the battery charger arrives, be sure to thoroughly read the manual in order to get accustomed to your new battery charger. Also, it is highly recommended to get a D+ ignition cable and, just in case, LC (current limiting) cable - both cables should be 18-16AWG copper cables.

Also, if You plan to charge a lead-acid battery, a temperature sensor is highly recommended.

Personally, if You are unsure how, let the certified professional do the job for You - often, it is the cheapest option in the long run.

Long Story Short: Renogy DCC1212-40 battery charger is a safe and reliable DC to DC onboard battery charger that is very similar to the Renogy DCC1212-20 (20A) and Renogy DCC1212-60 (60A) onboard battery chargers.

For more reviews and recommendations, feel free to check the Renogy 12V On-Board Battery Chargers Amazon link (link opens in the new window).