Renogy 40A DC to DC battery charger. Featured Image
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Our Honest Review Of The Renogy 40A DC to DC Battery Charger

Is the Renogy 40A DC to DC Battery Charger the best value charger for your campervan leisure batteries in 2023?

To help you decide, we’ve installed the charger in our campervan, ran tests and ironed out any technical queries.

The Renogy DC to DC charger is a worthy option for any campervan as it’s easy to install, performs exceptionally well, and is cheaper than its competitors.

To learn why we came to this conclusion, here’s our honest review of the Renogy 40A DC to DC battery charger, including why you should AND shouldn’t buy one.

Therefore, we’ve included some alternative DC to DC battery charger options if the Renogy charger isn’t suitable for you.

Portrait photograph of Jolly sipping a coffee

Trusted Review

Jolly (a self-confessed electrical geek with over 17 years of experience as a qualified electrical engineer) carried out the product review and testing.

His focus now is campervan conversion electrics which started in 2019 with the birth of Vandercamp. Jolly is either building his own campervan or providing electrical help and guidance to others.

The Renogy 40A DC to DC charger is installed on his current campervan powering a Renogy 200Ah Lithium Leisure battery. 


The product was purchased, installed and tested by us. Renogy does not sponsor the content of this post. Therefore, the review is our own honest opinion.

This post may contain affiliate links. Meaning, if you make a purchase after clicking one, we may earn some commission. This pocket money will help Vandercamp Adventures continue to grow at no extra cost to you. It’s a win win situation!! Learn More…

Renogy 40A DC-DC battery charger reviewed and tested blog graphic showing a picture of the charger

Table of Contents:

Where To Buy The Renogy 40A DC To DC Battery Charger

Renogy 40A DC-DC charger

Vandercamp Adventures Renogy Offers

Why We Chose The Renogy DC to DC Battery Charger

We required a DC-to-DC battery charger to charge our 200Ah Renogy lithium battery as a top-up when solar energy was low.

We needed a reliable charger that wouldn’t break the bank.

Renogy 40A DC to DC battery charger

Here are six reasons why we chose a DC-DC battery charger from Renogy:


We had a strict campervan conversion budget, and the Renogy DCC1212-40 was the least expensive out of comparable chargers. 

In addition, Renogy UK has regular offers.


Renogy is one of this sector’s biggest and most popular brands. We have years of experience installing and using Renogy products that have never let us down.

These Renogy products include:


The cable terminals, onboard switches and casings are robust and hard-wearing, so they’re built to last.

We’ve been using Renogy products for over 5 years+ now, and we’ve never had any issues with their build quality.

Technical Support

We’ve often relied on Renogy’s tech support for product-related technical queries to help design our campervan electrical systems.

Their technical support has always answered everything we’ve thrown at them within 2 days, but mostly by the next day.

However, some customers have reported that Renogy technical support has either taken a long time or has yet to respond.

Cable Terminations

Our battery cables are 35mm (starter battery to charger) and 25mm (charger to leisure battery). Therefore, we needed a unit that could accommodate these cable sizes.

When choosing a DC-DC charger, this is typically overlooked, so always study the manual and product specifications.

Renogy DC-DC battery charger output battery cable terminals

The cable terminals on the Renogy DC to DC battery charger are M6 bolts. These bolts will accommodate cables terminated with cable lugs and provide the most secure connection.

Therefore, the cable size has no restrictions, unlike other models (See comparison table).

D+ Ignition Wiring

The Renogy DC-DC charger requires an ignition cable to turn it on and off with the engine. Unlike other brands that have this feature built-in*.

This was a selling point because it lets us control the charger to optimise battery charging for all environments. We cover this in more detail below.

 *Some models require an ignition wire for smart alternators.

Further Reading | 6 Best DC To DC Battery Chargers For Campers 2023

Why We Chose A 40A DC to DC Battery Charger

The Renogy DC-DC battery charger is available in 3 models with different charge currents: 20, 40 and 60A. In fact, 5 output currents are available, including 10 and 30Amp; see the LC connection section below.

Renogy 40A DC to DC battery charger logo

Here are three reasons why we chose the 40Amp model:

1) Maximum Continuous Charge Current Of Our Battery

The DC-DC charger will charge our 200Ah Renogy lithium battery with a maximum continuous charge current of 100 amps.

Therefore the 40 amp charger is less than 100 amps, so it is suitable for charging our battery.

Lithium battery charge current is 50% of their capacity (always check the battery specification.)

Maximum Charge Current For The Renogy 200Ah Lithium Battery

2) Leisure battery charge time

We rely on the DC-DC charger in winter when solar energy is less efficient. The leisure battery must be charged enough to last us at least 1.5 days.

Our minimum daily usage is 40Ah per day, so we need 60Ah of battery power for 1.5 days.

The 40 amp charger will supply 40 amps power to the leisure battery every hour (Ah). So, a 1.5-hour journey will charge our 200Ah lithium battery by 60Ah.

Usage / Charge current = Battery charge time (Days)

60 (amp hours) / 40 (amps) = 1.5 (Days)

The 20 amp charger would need 3 hours of charge time to reach 60Ah. This charge time is impractical for us.

The 60 amp charger would need less than one hour so would be the most efficient. However, other factors must be considered.

3) Alternator charge current

Our alternator charge current is 110Amps. It uses approximately 35 amps to charge the starter battery and power the vehicle electrics during start-up. So, 75 amps are available.

However, alternators should never run at their total capacity (100%). Their rated charge current is so they can withstand the initial power surge during start-up rather than run continuously. Running at full power, or close to it, will lead to premature failure.

JOLLY NOTE: DC-DC charger inputs may experience a higher current than the rated output current by 50%.

For example, the 60Amp DC-DC charger output current is 60A, whereas the input current may be up to 90Amps. Therefore, this factor must be considered when choosing a DC to DC charger and cable calculations.

See table below

The 40A charger could have a current draw on the alternator of 60A. This is less than the total remaining capacity of the alternator (75 amps) during start-up.

The 20A charger could have a current draw on the alternator of 30A, so it would put little stress on the alternator. 

Alternatively, the 60A charger could have a current draw of 90A, so it would exceed the maximum capacity of the alternator. 

This table shows the potential start-up current of the DC-DC chargers:

ModelRated charge currentStartup current draw (>50%)Continuous current draw

Therefore, we chose the Renogy 40Amp DC-DC charger because it compromises alternator efficiency and charge time to suit our needs. 

20 Amp charger – Kinder to the alternator but wouldn’t charge the leisure battery enough. The DC-DC charger is our primary power source in the winter, so we need a higher charge current.

60 Amp charger – This would charge the leisure battery the fastest but put too much strain on our alternator. 

40 Amp charger – The perfect compromise between leisure battery charge time and alternator efficiency.

Unboxing Video

Product Details and Specification

NOTE: The information below is sourced from the Renogy 40A DC to DC charger product page. 

Key Features

  • Compatible with multiple battery types – AGM, Flooded, Gel, and Lithium batteries.
  • Compatible with traditional and smart alternators.
  • 3-Stage charging (bulk, boost and float).
  • Charge a leisure battery to 100% state of charge.
  • Smart protection features (isolated, over-voltage protection, over-temperature protection, and reverse polarity protection.
  • Starter battery over-discharge protection.
  • Leisure battery charge current protection (LC connection).


Renogy 40 Amp DC to DC charger specification table
Image taken from the Renogy DC-DC Charger product page.

Manual Download



Manual Book

Manual Book – before 03/25/2020


Product Manual Queries Answered

Some parts of the Renogy DC-DC charger product manual are overly technical and could be clearer, so we contacted Renogy support for clarification.

This information is in addition to the information in the manual.

D+ Ignition Wiring

The D+ ignition turns the charger on when 12 volts is applied. Ideally, the 12 volts will come from the vehicle’s ignition circuit, so the charger will turn on/off with the engine. 

However, locating a vehicle’s ignition circuit is tricky and may require understanding schematic drawings of the vehicle’s electrics. These can be found in HAYNES manuals and online. 

Renogy DC-DC battery charger D+ cable connection point

This could sway people to other products where the ignition wiring isn’t required. However, this feature is one of the reasons why we have the Renogy 40A DC to DC battery charger. Here’s why:

Reason 1 – We plan to use the DC to DC charger during the winter when solar energy is low and as a backup charge source. Therefore, we can manually turn the charger on/off via a switch on the D+ wiring.

For example, our solar system will generate enough power to charge the leisure battery in the summer months, so the DC-DC charger won’t be required. Do other models have an on/off switch? 

Reason 2 –To reduce the strain on the alternator during engine start-up. We switch on the charger approximately 5-10 minutes after starting the engine. This allows the alternator to charge the starter battery and deal with the initial high current flow as the vehicle electrics turn on. 

The current on the alternator will have reduced once the charger is switched on. Therefore, by reducing the load on the alternator, we help prolong its life. 

Reason 3 – Turn the charger off for short, stop-start journeys. The Renogy charger is designed to go through a 3-stage charging method that it won’t achieve on short journeys.

Therefore, we turn the charger on for journeys of 30 minutes + to ensure the battery gets a healthy charge. 

JOLLY NOTE: Even if you connect the charger to the ignition circuit, I recommend installing a switch to manually turn on/off the charger for maintenance and the reasons given above. 

LC Current Limiting Wiring

LC stands for current limiting, so it will reduce the rated output current of the DC-DC charger (20/40/60A) by 50%.

Renogy DC-DC battery charger connecion points for the D+ ignition and LC cable terminals

Why would you want to reduce the output current of the charger? Isn’t it easier and cheaper to use a lower-rated charger?

Here are two reasons why you may need the LC connection:

1) To get a broader range of output currents to meet your specific needs.

The Renogy DCC1212 battery charger is available in 3 models; 20A, 40A and 60A. But with current limiting, the Renogy DC to DC charger has 5 possible output currents; 10, 20, 30, 40 and 60A.

Similar products only have 1, 2 and 3 output current options. 

A chart showing the current limit capabilities for the 20, 40 and 60 amp renogy dc to dc charger models
LC current limiting chart from the user manual (page 14)

Similar products only have 1, 2 and 3 output current options. 

2) To future proof your electrical system

You may have designed your campervan electrics to have more battery capacity in the future. Or, you want peace of mind that if you upgrade the leisure battery, the DC to DC charger won’t need replacing. Or, you’re on a tight budget and can’t afford a larger capacity battery just yet.

For example, say you only need 100Ah of battery capacity now but will require 200Ah in the future. The 60Amp charger would be ideal; you couldn’t charge the 100Ah battery with 60Amps, but you could with 30Amps by reducing the current by 50%. Then, once the battery capacity has been increased to 200 amps, the charger could run at 100%, delivering 60 amps

DIP Switch Setting

The Renogy DC to DC charger can be configured to charge all lead-acid and lithium batteries. There are DIP switches on the charger to set the type of battery it is charging.

Renogy DC-DC battery charger DIP switches
Dip switches set to supply a charge voltage of 14.4 volts to our lithium iron leisure battery

The DIP switches are straightforward to set, and the manual explains this well; however, the table for setting lithium batteries could be clearer.

Therefore, we contacted Renogy support to confirm the settings and designed a simplified version of the table:

Lithium Battery VoltageSW1SW2SW3SW4SW5

It’s crucial to set the correct charge voltage for YOUR battery. Over or undercharging a battery will affect its performance and lifespan. Battery charge voltage can be found in the manual, but contact the supplier/manufacturer for clarification. 

For example – Our Renogy 12v 200Ah lithium battery has a charge voltage of 14.4v. It’s stated in the manual and confirmed by Renogy support.

Renogy DC-DC Charger Manual Page-15

For example –The Victron 12v 90Ah AGM deep cycle battery charge characteristics are shown in the datasheet.

Victron AGM Leisure Battery Charge Characteristics


Typically, campervan conversions use the metal chassis as the common grounding point for the vehicle electrics, including the leisure battery. Therefore, the system will work if all ground cables are connected directly to the chassis via the battery terminals or ground busbars.

However, it’s worth noting that the Renogy DC-DC charger is an ISOLATED charger, as confirmed by Renogy support. 

This means the input ground and output ground terminals are not connected inside the charger. 

The manual states, “The DC-DC share a common negative ground…” which is misleading because isolated chargers’ input and output grounding terminals are not connected/shared within the charger. See the diagram below:

Alternatively, NON-Isolated chargers’ ground points ARE connected together.

Specific installations require ISOLATED chargers if the output source requires a floating ground, is sensitive to ‘noise’ and for safety reasons. 

Wiring And Fusing

When calculating the cable size for a DC to DC charger, its commonly overlooked that the DC input may experience a higher current draw than the rated DC output by up to 50%. 

For example, the Renogy 40A DC to DC battery charger may draw up to 60Amps whilst charging (40 amp x 1.50 (50%) = 60 amps).

Considering this when calculating cable sizes will avoid voltage drop and overheating complications.

This is stated in the manual but can easily be overlooked, so the cable and fuse size chart is a good reference point.

In addition, we recommend doing cable calculations to ensure all factors are considered. If in doubt, go a size bigger on the cable to reduce the voltage drop and prevent cable overload.

Product Testing

Once we installed the Renogy 40A DC to DC charger in our campervan, we performed some basic tests. These show how our charger performs in real-life situations.

Renogy 40A DC-DC battery charger on a table with a cable crimper, digital multimeter and wire cutters

We did the tests multiple times over several days to give a more accurate average result. For each test, all vehicle electrics were switched off (e.g. lights, radio, heater etc.), and the leisure battery wasn’t fully charged.

A clamp meter and multimeter were used to measure the current and voltage on both the input and output cable terminations.

Test 1) Input voltage

The input voltage to the charger from the alternator was 14.4v. This is measured by testing the battery positive and negative terminals with a volt meter (set to DC volts).

Test 2) Current draw during start-up with the charger switched on.

During start-up, the current draw on the alternator jumped up to 79.6 amps. Then, it declined to 48.7 amps over 30 seconds and fluctuated between 48-49 amps.

Test 3) Current draw during start-up with the charger turned on after 5 minutes.

During start-up, the current draw on the alternator jumped up to 41.2 amps for a split second and then dropped to 23.5 amps. Then, the current draw declined from 23.5 amps to 6 amps over 60 seconds, where it settled.

Five minutes after the initial start-up, the charger was switched on. The current draw rose to 50.7 amps for a split second, then settled at 39-40 amps.

Test 4) Output current

The output current measured between 39 and 40 amps when the charger was switched on.

This test has proven the Renogy charger produces 40 amps output current, which is an outstanding performance, especially from a low-budget DC-DC charger.

Pros And Cons


  • Charger current efficiency of 90%.
  • Cheaper than the competition with similar/better performance.
  • Simple installation and setup.
  • The only charger with 5x DC output current configurations.
  • Knowledgeable and timely technical support.


The Renogy DC to DC Charger Is Most Suitable For:

  • Low budgets – The Renogy DC-DC charger is less expensive than similar chargers without compromising quality.
  • Charging all battery types (lead-Acid and lithium) and capacities.
  • Future-proofing for an increase in battery capacity by using the LC connection.
  • A secondary charging method- It can be manually switched on/off when required using the D+ ignition connection..

The Renogy DC to DC Charger Is Unsuitable For:

  • Installers with little/no electrical knowledge or skills > the ignition (D+) wiring can be complicated; other models have a built-in voltage sensing system.
  • External monitoring requirements – this charger is stand-alone. Other chargers offer Bluetooth connectivity and remote switching. Alternative product – Victron Orion-Tr Smart.
  • 24v electrical systems and 24v alternators – the unit works with 12v systems only. For 24-volt systems, you need a 24 – 12v converter. Alternative product – Redarc BCDC12 charger 
  • No budget restrictions – there are other products with more features*. See alternative product table.

*Our opinion is based on extensive research of alternative products

Alternative DC To DC Charger Features

The Renogy DC to DC charger is a simple battery charger that works well. However, alternative products have additional features that may appeal more to you.


Some DC to DC chargers have built-in MPPT solar charging, so one product can charge your leisure battery with solar and alternator power. This has become a preferred method of charging because you only need to install one product, and it’s cheaper than buying a DC-DC charger and solar charge controller separately.

However, if the product fails, you lose two means of charging. Also, the power outputs are more restricted than separate units.

We recommend the Renogy 50A DC-DC onboard charger with MPPT.

Further Reading | Charge Your Leisure Battery With Solar Power

Remote Monitoring

Some products have Bluetooth, allowing you to access settings, adjust parameters and control the charger remotely.

This allows you to closely monitor and change settings to ensure you get the best out of the charger.

However, this is an over-complication if you want a simple battery charger. Also, if you’re a geek like Jolly, you’ll get monitoring addiction.

We recommend the Victron Orion-Tr Smart with its quality Bluetooth monitoring App.

Further Reading | 4 Ways Of Monitoring The Charge Of Your Leisure Battery

5-Stage Charging

5 Stage charging includes the 3 stages of charging (bulk, absorption and float) with the addition of:

  • Desulphation (lead-acid batteries only) – removes sulphate from the lead plates of the battery, restoring the battery capacity.
  • Accept (lithium batteries only) – Tests if the battery can accept a charge to prevent the charging of a defective battery.
  • Pulse – Maintains the battery at 95–100% capacity, giving a pulse when necessary to keep the battery fully charged.

5-stage charging is a good option if you have lead-acid batteries as it will maintain their health and prolong their life better than 3-stage charging. However, it does come at a cost.

We recommend the Ctek D250 SE and Smartpass 120S.

Voltage Sensing Relay Software

Some chargers have voltage sensing software that automatically triggers when they receive a charge voltage from the alternator, turning the charger on/off.

However, this automated on/off triggering can be unhealthy for your battery on shorter journeys.

Alternative Product Comparison Table

Here’s a table comparing best alternatives to the Renogy 40A DC to DC Battery charger:

ProductMaximum Charge Current (Amps)12v/24v CompatibleCostMPPT SolarIn-built voltage sensingIsolated/Non-IsolatedRemote monitoring/switchingOther FeaturesView Product
Renogy DCC12-12-20/40/60Renogy 40A DC-DC charger20/40/60A (10/30A*)12v£100-£160+Isolated*Charge current with LC connection.
Low charge current setting (LC)
View Renogy Product
CTEK D250 SECTEK D250SE DC to DC battery charger20A12v£250-£270
Non-Isolated (common ground point)Separate system monitor*Ignition wiring required for smart alternators
- 5-Stage charging
- Starter battery charging when leisure battery is full
- Combine with Smartpass 120S for large battery banks (100-800Ah)
View Ctek Product
Victron Orion-Tr SmartB2B/DC-DC leisure battery charger18/30A12v & 24v£160-£300Isolated/Non-isolatedBluetooth App- Wire in parallel to increase output
- Remote on/off
View Victron Product
Sterling BB1230, BB1230+MPPT, BB1260Sterling BB1230 DC to DC charger30/60A12v£190-£300✔ (30A only)Non-isolated (common ground point)Remote control available- MPPT model prioritizes alternator charging over solar.
- Quiet run setting
View Sterling Product
Redarc BCDC 1225D, 1240D, 1250DRedarc BCDC1240D 40A DC DC Charger MPPT Solar Controller20/40/50A12v & 24v£380-£500✔*Non-isolated (common ground point)Optional external LED*Ignition wiring required for smart alternators
- Tested in Australian outback in extreme conditions (moisture, dust, vibration).
View Redarc Product
Renogy DCC50SRenogy DC50S DC to DC charger with MPPT Solar 50A (25A solar/25A alternator)12v£210+IsolatedRenogy DC Home bluetooth app- MPPT solar prioritizes the leisure battery.
View Renogy Product

* We recommend these products based on research into the product specification, features and other people’s knowledge. We have not used or installed all of these products.

Further Reading | Discover The Best Campervan DC to DC Battery Chargers For 2024


What Size DC-DC Charger Do I Need?

This will depend on a few factors; 

  • the Ah rating of your leisure battery bank, 
  • how fast do the batteries need to charge?
  • your budget,
  • vehicle alternator power,
  • and journey times.

We recommend choosing the lowest power charger that will give you enough charge in your batteries rather than a higher power charger that will charge the batteries faster.

Why? Two main reasons; 

1) The more power drawn from an alternator will result in faster deterioration, 

2) Generally, batteries prefer lower current charging over a prolonged period rather than high current fast charging as this will prolong the battery’s life*.

*This will affect each battery type differently.

This is why we chose the 40A Renogy DC to DC charger and have a lithium battery.

Further Reading | What Size DC to DC Charger Do I Need? A Step-By-Step Guide

How Fast Will It Charge My Leisure Battery?

Put simply, the more current flow into a battery, the faster it will charge.

For example, a 100Ah battery charged with 10Amps will take 10 hours to charge to 100% (100Ah / 10A = 10hrs). Likewise, a 100Ah battery charged with 40Amps will take 2.5 hours to charge to 100% (100Ah / 40A = 2.5hrs).
These are basic guideline figures; other factors will affect charging times.

However, regular high-current charging is only recommended for lithium batteries. Lead acid batteries can deteriorate faster, reducing their lifespan. So, choosing the right size charger is crucial for your battery health.

Can Anyone Install A DC-DC Charger?

Yes, you don’t need to be an electrician to install a campervan DC-DC charger.

However, you must follow ‘good electrical practice’ and the current electrical regulations. 

D+ Ignition Connection – what is it and is it required?

The D+ connection is the on/off switch for the Renogy DC to DC battery charger. It requires a wired connection to your vehicle’s ignition wiring so it can turn on and off with the alternator……read more

Sound too complicated? Don’t worry. There is another method

What Size Cables Do I Need?

Cable sizes are noted on page 09 of the manual. However, these figures should be used as a guide, and cable calculations must be carried out to determine the correct cable size for your system.

See the cable and fuse size table above.

Using the correct size cable is fundamental to safety – there’s a risk of excessive voltage drop and overheating if the cables are too small.

However, big cables are more expensive, more challenging to work with and may not fit into the DC-DC charger terminals. Thankfully, the Renogy DC to DC chargers can accommodate larger cables than other similar chargers.

What’s The Difference Between Isolated & Non-Isolated Chargers?

An isolated power converter isolates the input from the output by electrically and physically separating the circuit into two sections preventing direct current flow between input and output

Isolated Chargers

The input DC ground is not connected to the output DC ground within the charger; they are isolated. Typically required when the item being charged has a separate common ground to the DC input (starter battery), so they’re not connected.

For example – when charging a portable power supply, the negative won’t be connected to the vehicle chassis. Therefore, isolated chargers can break up ground loops and provide a floating output.

Not commonly used in campervans because the starter and house batteries are typically grounded to the same point (chassis), so have the same ground loop.

A drawing to show the ground points aren't connected within an isolated DC-DC battery charger
How an Isolated DC-DC battery charger ground works

Non-Isolated Chargers

The DC input and DC output ground wires are connected within the charger; they are not isolated. Typically required when the item being charged has the same common ground as the DC input (starter battery), so they’re connected.

For example – when charging campervan leisure batteries where the ground wires are connected to the vehicle’s chassis.

Use when an isolated charger is not required. Also, non-isolated chargers are generally cheaper, smaller and more efficient than isolated chargers.

However, the Renogy charger is the best of both; it’s low-cost and isolated.

A drawing to show the ground points are connected within a non-isolated DC-DC battery charger
How a non-Isolated DC-DC battery charger ground works

JOLLY NOTE: Isolated chargers will work in non-isolated systems but not the other way around. The Renogy DC-DC charger is isolated, so it will work in all situations.

Is It Isolated Or Non-Isolated

“For added safety to personnel, the DCC12-12 isolates the input from the output, preventing incorrect voltage transmission.” 

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

It’s isolated, as stated in the website description, manual (P11) and confirmed by the Renogy support team.


The Renogy 40A DC to DC charger is an excellent choice for any campervan conversion. As well as being easy to install, it’s less expensive than its competitors without compromising quality.

It’s easily a contender as the best value charger for your campervan leisure batteries in 2023.

Our review is an honest summary of our experiences with the Renogy DC to DC charger for full-time vanlife in our off-grid Luton campervan conversion.

Still unsure? Check out the 6 best DC-DC battery chargers for campervans.

Renogy 40A DC To DC Battery Charger

Renogy 40A DC-DC charger

Vandercamp Adventures Renogy Offers

See Current Price

Other Renogy DC-DC Battery Chargers