renogy|SKU:099--0

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

Charge Your House Batteries Directly from the Starter

Charges while you drive — Tops off house batteries from your starter battery
Works with any chemistry — Supports AGM, Flooded, Gel, and Lithium
Smart 3-stage charging — Bulk, Boost, and Float for a full charge
Built-in safety protections — Over-voltage, over-temperature, and reverse polarity shielding
  • FREE System Design Consultation -- Confirm compatibility with your alternator and battery setup
  • FREE Shipping -- Ships free to your door, no minimum order

$149.95

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Renogy 12V 40A DC to DC On-Board Battery Charger
Renogy 12V 40A DC to DC On-Board Battery Charger
$149.95

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Renogy 12V 40A DC to DC On-Board Battery Charger
Renogy 12V 40A DC-DC On-Board Battery Charger
$149.95

Charge Your House Batteries Directly from the Starter

The most effective way to keep your house batteries topped off while driving. This Renogy DC-DC charger pulls from your starter battery and delivers clean, 3-stage charging to AGM, Flooded, Gel, or Lithium banks — so your off-grid setup is ready the moment you arrive. It's a field-tested, grid-independent charging path that isolates input from output, protecting your starting system from voltage errors. Over-voltage, over-temperature, and reverse polarity protection are built in. Compact and CE-certified, this unit is built-to-survive the demands of mobile power systems.

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Multi-Chemistry Charging
3-Stage Smart Charge
Starter Battery Protection
CE Certified Quality
12V
System Voltage
40A
Charging Output
3-Stage
Charging Profile
One Charger, Every Battery Chemistry You Run

One Charger, Every Battery Chemistry You Run

Most off-grid builders have been burned by a component that looked right on paper but didn't play nice with their battery bank. This Renogy DC-DC charger eliminates that risk. It supports AGM, Flooded, Gel, and Lithium deep cycle batteries — so you are not locked into one chemistry. At Off Grid Vault, we vet every product for real-world compatibility before it hits our shelves. This charger works with a multitude of alternator types, so it integrates into your existing setup without voltage mismatches or protocol conflicts. No mix-and-match guesswork. Just proven charging that actually delivers.

3-Stage Charging Gets You to 100% Automatically

3-Stage Charging Gets You to 100% Automatically

This charger does not just dump current into your house batteries and hope for the best. It runs a proper 3-stage charge cycle — Bulk, Boost, and Float — so your batteries reach a full 100% charge without overcharging or undercharging. For LiFePO4 owners, this matters. Proper float voltages extend cycle life and protect your investment. The charger also isolates input from output, preventing voltage transmission errors that could interfere with your house bank. Over-voltage protection, over-temperature protection, and reverse polarity protection are all built in. CE certified. This is field-tested hardware, not a roll of the dice.

Starter Battery Protection While You Drive

Starter Battery Protection While You Drive

Nothing stops a trip faster than a dead starter battery because your house bank drained it. This Renogy charger monitors whether your generator is running and prevents over-discharge of the starting battery. You drive, it charges the house bank safely, and your starter battery stays ready to crank. The compact, robust design handles the vibration and temperature swings of real-world vehicle and RV installations. Whether you are running a cabin build, an overland rig, or a homestead auxiliary system, this charger keeps your starting power protected. Off-grid proven for the conditions that actually matter.

System Compatibility

Verify these conditions before adding to your build.

  • 12V DC vehicle or alternator system
  • House battery bank using AGM, Flooded, Gel, or Lithium chemistry
  • Starter battery present as charge source

Where This Charger Belongs

Built for mobile and remote power systems that need reliable house battery charging on the go.

Van & RV Conversions
Off-Grid Cabin Access
Marine House Banks
Overland & Expedition Builds

Full specifications

At a glance

Dimensions
See product page
Power
12V
Compliance
CE
Warranty
See product page
Full specifications9 data points across 4 categories

Dimensions

Overall DimensionsSee product page
WeightSee product page

Power & Performance

System Voltage12V
Charging Output40A
Charging StagesBulk, Boost, Float
Compatible Battery TypesAGM, Flooded, Gel, Lithium

Materials

HousingSee product page

Compliance & Warranty

CertificationCE
WarrantySee product page

The Off Grid Vault Promise

Every product we carry is vetted for real-world off-grid performance. If it doesn't meet our standards, it doesn't make the cut.

Free ShippingShips free to your door — no minimums, no thresholds, no fine print.
30-Day Performance GuaranteeIf it doesn't perform as specified, we make it right. Uninstalled returns accepted within 30 days.
Free System Design ConsultationOur engineers size your system for your actual consumption — no guesswork, no incompatible components.

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

Highlights: 

  • Compatible Multiple Battery Types – Compatible with a multitude of alternator types, the DC-DC battery charger offers correct charging for AGM, Flooded, Gel, and Lithium batteries.
  • Smart 3-stage Charging – The DC-DC battery charger will charge your house batteries from the starter battery by 3-stage charging (Bulk, Boost, and Float), to make sure it optimally and automatically charge to 100%.
  • Various Protections For Ultra Safety – Offers Over-voltage Protection, Over-temperature Protection, and Reverse Polarity Protection to ensure the operation safety. It also isolates the input and output to prevent voltage transmission errors and interfere with house battery charging.
  • Protect Your Starter Battery – The DC-DC battery charger is capable of identifying whether the generator is started, to prevent over-discharge of the starting battery and protect the generator.
  • Reliable Quality – The compact and robust design makes it suitable for all conditions. CE certification.

Description:

The DC-DC Battery Chargers are the most effective way to charge your house batteries from the starter battery. Compatible with a multitude of alternator types, the DC-DC battery charger offers correct charging for AGM, Flooded, Gel, and even Lithium deep cycle batteries! Featuring a 3-stage battery charger and multiple electronic protections, users can feel confident that their batteries are being charged optimally and automatically. For additional safety, it isolates the input from the output preventing incorrect voltage transmission. Easily install the compact yet sturdy DC-DC battery charger on RV’s, commercial vehicles, boats, yachts, and many more applications!

Compatible Multiple Battery Types

Compatible with a multitude of alternator types, the DC-DC battery charger offers correct charging for AGM, Flooded, Gel, and Lithium batteries.

Smart 3-stage Charging

The DC-DC battery charger will charge your house batteries from the starter battery by 3-stage charging (Bulk, Boost, and Float), to make sure it optimally and automatically charge to 100%.

Various Protections For Ultra Safety

The DC-DC battery charger isolates the input and output to prevent voltage transmission errors and interfere with house battery charging. It has multifunctional safety technology including over-voltage protection, over-temperature protection, and reverse polarity protection to make it safer for use.

Protect Your Starter Battery

This Renogy DC-DC battery charger is compatible with traditional and smart alternators. The D+ Ignition cable is capable of identifying whether the generator is started, to prevent over-discharge of the starting battery and protect the generator. 18-16AWG copper cable recommended.

Please note the D+ Ignition Cable is not included.

Protect Your House Battery

The LC wire can automatically adjust the charging current to prevent excessive charging current from damaging the house battery. 18-16AWG copper cable recommended.

Please note the LC cable is not included.

Prolong Battery Lifespan

The charger needs to select the charging mode according to the battery voltage. By utilizing the DC-DC temperature sensor, this charger is able to protect your battery from high or low temperature by giving -3mV/°C/2V compensation so that the charger recognizes the voltage more accurately and assures stable and constant charging to the battery.

Please note the temperature sensor is not included and it cannot use with Lithium batteries.

This diagram shows the whole connection of the DC-DC On-Board Battery Charger. 

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About renogy Battery Chargers

renogy is a trusted manufacturer of premium battery chargers. OffGridVault is an authorized dealer offering the full renogy lineup with free delivery, price match guarantee, and expert support.

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