Renogy 12V 40A DC to DC Battery Charger

The Renogy 12V 40A DC to DC Battery Charger Charges Your House Battery While You Drive and Stops When the Engine Does

The Renogy 12V 40A DC to DC Battery Charger charges a 12V auxiliary battery from a vehicle's alternator at up to 40A and 584W. Renogy rates its charging efficiency at 94%, and it works with AGM, gel, flooded, sealed lead-acid and lithium iron phosphate batteries.

It's made for RVs, vans and small boats that run a second battery for lights, a fridge or electronics. It works with traditional and smart alternators, and its alternator running detection protects the starter battery.

Renogy 12V 40A DC to DC Battery Charger Features

Alternator Running Detection

Charging continues only while the alternator is running, and it stops when the alternator stops. Renogy says the charger adjusts its charging mode at startup to protect the starter battery.

Traditional and Smart Alternators

Renogy lists an alternator input of 13.2-16.0VDC for traditional alternators and 12-16.0VDC for smart alternators (Euro 6). Smart alternators need the IGN signal wire, which is included. Traditional alternators don't need it.

Five Battery Types

Choose AGM/SLD, GEL, flooded (FLD), lithium (LI) or a user mode with the Type button. For lithium, lithium battery activation can be turned on or off. The charger also has an RS485 communication port.

Temperature Sensor for Lead-Acid Batteries

The included 2 m sensor reads the battery's surroundings and adjusts the charge voltage when the battery is cold. Renogy says not to use it on a LiFePO4 battery that has its own BMS, and the sensor port works with lead-acid batteries only.

Protections and Heat Handling

Protections include reverse polarity, overvoltage, over discharge, overcurrent and over temperature. In high-temperature conditions the charger reduces output to charge safely. Renogy calls the case corrosion-resistant and suited to small boat cabins and humid marine spaces.

Compact Layout With Spaced Terminals

The charger measures 9.31 x 6.00 x 2.30 in. Input and output terminals are spaced apart to reduce short-circuit risk.

Real-World Applications

RV and van house batteries. Charge a 12V lithium or AGM house battery from the alternator on the road.

Smart alternator vehicles. Connect the IGN signal wire so the charger knows when the engine is running.

Small boat cabins. Renogy points to small boat cabins and humid marine environments for its compact case.

Practical Comparison

40A Output Versus a Lower-Output Charger

A higher-output charger can refill a house battery faster while the alternator runs, but it needs heavier cable and fuses. This charger's quick guide calls for 8 AWG cable on the auxiliary battery side and 6 AWG on the starter battery side.

DC to DC Charger Versus a Direct Connection

A direct connection passes the alternator's voltage to the house battery as is. This charger runs a charge profile for your battery type and stops when the alternator isn't running.

Buyer Guidance

Wiring, Fuses and Alternator Limits

Renogy's quick guide calls for 8 AWG cable and a 40A ANL fuse on the auxiliary battery side, with cable no longer than 3 meters. On the starter battery side it calls for 6 AWG cable and an 80A ANL fuse. Before installing, check with your vehicle manufacturer that the alternator power doesn't exceed 720W with output current in the range of 75A to 100A. Leave 5.91 in (150 mm) of clearance on all sides. Fuses and cables aren't included.

Monitoring Needs a Bluetooth Module

To monitor in the Renogy app, add Renogy's BT-2 Bluetooth module to the communication port. It's not part of this option.

This May Be A Good Fit If

• You charge a 12V house battery from an alternator
• You want protection for the starter battery
• Your vehicle has a smart or traditional alternator
• You use AGM, gel, flooded or lithium batteries

Common Questions

What Batteries Does It Charge?

By default it supports 12V AGM, flooded lead-acid, gel, sealed lead-acid and lithium iron phosphate. A custom mode lets you adjust settings.

How Do I Get Communication?

Renogy says to connect its BT-2 Bluetooth module to the communication port. That links the charger to the Renogy app and ONE Core.

Any Installation Tips?

Mount the charger horizontally for better venting and heat dissipation, and place it near the service battery.

What's Included

• 1 x Renogy 12V 40A DC to DC Battery Charger
• 1 x Battery Temperature Sensor (2 m)
• 1 x IGN Signal Wire (3 m)
• 4 x Terminal Rings
• 4 x Mounting Screws
• 1 x User Manual

Alternator Charging Built for Heavier Loads

The Renogy 12V 40A DC to DC Battery Charger gives your house battery a managed 40A charge from the alternator and stops when the engine stops. If you'd like help with cable, fuse and alternator questions, the Outbound Power team is happy to help.

Renogy 12V 40A DC to DC Battery Charger Manual