How to choose the best vehicle battery charger: What's available?

Solar ChargingSolar Charging

Last week we covered the things you should consider for your dual battery setup in your vehicle such as the type of vehicle, alternator, electrical accessories you want to run and the length of time that's going to be spent free camping.

In this blog, we’ll delve a bit deeper into why these factors are important and as a result, will help you decide the best dual battery system for your setup.

We'll talk a bit more about the three main types of battery chargers on the market; Smart Battery IsolatorsDual Battery Chargers, and Battery Management Systems.


Smart Battery Isolators

Smart Battery Isolators have been used for a number of years and offer an effective approach for using your vehicle’s alternator to charge the second battery whilst the vehicle is running. Its job is to also protect the start battery from going flat by isolating it from the secondary battery when the engine is turned off.

A battery isolator will recognise when the vehicle engine is running and charge is going to the starting battery via the vehicle’s alternator. It will do this by sensing battery voltage, and when the start battery reaches 13.2 volts on a 12-volt system, it will connect and start charging the secondary battery.

The Smart Start SBIThe Smart Start SBI

The Smart Start SBI; REDARC's Smart Battery Isolator

When the engine is turned off, and therefore the alternator is no longer running, once the start battery drops below 12.7 volts the isolator will disengage the secondary battery. This will stop any loads connected to the auxiliary battery from also draining the battery.

A good analogy for this is to think of the Battery Isolator as a tap between the batteries and the alternator is a pump feeding the start battery. Once the pump (alternator) fills the start battery to a point (13.2v) the isolator detects this and turns on, allowing the feed going into the first battery to pass onto the secondary battery. Therefore the pump feeds both batteries at the same time.

The Smart Start SBIThe Smart Start SBI

This type of setup is recommended for vehicles that have a fixed vehicle alternator, can be installed under the bonnet and if you’re on a budget. If your setup meets none of these criteria, the next level up is an In-vehicle battery charger, also know as a DC-DC battery charger.


DC-DC Battery Charger

Generally, a DC to DC battery charger is going to offer more flexibility for your dual battery setup, not only in terms of correct charging for your specific battery, but also suitability for different alternator types, installation location, and amp size. Some even accept additional power sources such as solar.


Why they are better

The problem with using your vehicle’s alternator as the main charging source for a secondary battery is that a majority of vehicle alternators after 2010 do not put out more than around 14V after driving the vehicle for 10 – 25 minutes. Deep cycle batteries, which are predominantly used as secondary batteries, generally require charging at higher voltages which mean if they are being charged solely by the alternator they're often left undercharged.

Providing the correct charge to a battery is a bit like filling your tank with the correct fuel for your engine. You wouldn’t use diesel in your petrol engine and on the higher end of the scale you would be better off supplying high octane fuel to a performance petrol engine.

BCDC In-vehicle battery chargerBCDC In-vehicle battery charger

BCDC In-vehicle battery charger

Therefore, a DC-DC battery charger is recommended as it is designed to effectively charge a secondary battery to 100% ensuring the prolonged life of your secondary battery. An In-vehicle battery charger applies the correct voltage level to achieve a full state of charge, while controlling the amount of current flowing into the battery, so that it doesn’t charge too quickly and cause unwanted damage.

An In-vehicle battery charger may also be necessary when you have to install the secondary battery away from the alternator due to space restrictions under bonnet, as a DC-DC battery charger can overcome voltage drop from long distances. Which is becoming increasingly common in modern vehicles. In addition, quality DC to DC battery chargers are designed to also work with any type of alternator or vehicle voltage as it can operate and sense a wide voltage range.

If you’re after a charger that can be mounted under your bonnet, the BCDC Classic is the way to go. Fully sealed against dust and water, it can handle all the under-bonnet heat and deep-water crossings any trip can throw at it. There’s no need to worry about your charger being knocked about on corrugated tracks, you can get to your destination and back safely with the BCDC Classic.

For a charger that can be mounted in the cabin or canopy of your vehicle, the BCDC Core could be a good option. Tuck it away in a side panel, hide it under the rear floor or stow it under the seats to make your power setup look like it was meant to be there.


Finding the correct size dual battery charger

If you are thinking of going down the DC-DC charger route, then also consider the amps required. Dual Battery Chargers typically range from 6 – 40 amps. So, how do you know which one is right for you?

As a general rule, battery bank sizes of 75-200AH require a 25-amp dual battery charger and then for higher capacity needs, a 40-amp dual battery charger is recommended. Why is this important?

Excessive current flow into a battery can impact it in a manner of ways, the worst of which can be the degradation of battery service life and capacity. That is why it is imperative to work out the accessories you wish to run when you go camping, then work out the battery capacity required and select the right sized dual battery charger based on those needs. Otherwise you may just end up wasting time and money.


A word on solar

Finally, lets consider that many DC-DC chargers can now accept solar as a charging method for your secondary battery, thanks to in-built solar regulators. This has the added benefit of providing less load on your vehicle’s alternator and is especially handy if you’re planning to stay in one location for an extended period of time, and don’t wish to drive and engage the alternator to get the batteries back to full charge.

folding solarfolding solar

Portable solar panels are a great way to keep charge of your vehicle's battery

The BCDC Dual Input range from REDARC for example, is able to charge batteries from solar (with Green Power Priority) and the vehicle’s alternator simultaneously. It works with all alternator types including smart alternators and with a range of battery types including lithium iron phosphate.


Battery Management Systems 

If you really want to get the most of out of your dual battery setup, then the crème de la crème would have to be a battery management system.

A battery management system has all the bells and whistles, combining the features and benefits of a Smart Battery Isolator, Dual Battery Charger and more. The Manager30, for example, is six products in one and offers a variety of features unlike anything else in the market. Its features include;


-          DC-DC Battery Charger

-          240V charger

-          Battery Isolator

-          Load Disconnect Controller

-          MPPT Solar regulator

-          Remote Monitor

The Manager30 The Manager30

The Manager30 lets you see how your battery is charging and monitor where the charge is coming from 

Green Power Priority 

The Manager30 has a high-performance MPPT Solar Regulator that ensures you can extract every last watt available from your solar panels throughout all conditions. Normally with most systems you would need to choose whether to take power from your solar panel, or the vehicle charging system, or from 240V, however with the Manager30 it can accept all available power from the solar panels first, before using the vehicle’s alternator or 240v power. This means that the vehicle has less work to do when solar is available, meaning fewer emissions and more fuel consumption savings.


Load Disconnect Controller

The Manager30 Load Disconnect Control has the added benefit of ensuring your batteries are not over-discharged by your loads, warning you when the battery is nearly flat so you can take action to remain powered up.

If your loads do turn off because you weren't present when the warnings occurred, The Manager30 allows you to over-ride the Load Disconnect and get power back for a further 10 minutes. This allows you to get a charge source started so you are not caught out fumbling around in the dark.

The Manager30The Manager30

The Manager30 Battery Management System

Lithium Battery Charging Profile 

LiFePO4 batteries can be a third of the weight and physical size of a lead acid battery of comparable storage capacity, and their cycle life can be up to 10 times greater than a lead-acid battery. Another functional advantage is that they are capable of delivering more usable amp hours, nearly double that of a lead-acid by allowing deeper discharge at a usable voltage.

This means that your loads run better, have brighter lighting and more efficient cooling or heating throughout the operating range of the LiFePO4 battery. Couple this with the 30A charge rate, new LiFePO4 charge profile and advanced monitoring of The Manager30, means you can have the ultimate combination of charging, monitoring, load control and storage.

So there you have it, a beginners guide to vehicle battery chargers. You can spend hundreds of dollars on high-quality batteries for your touring setup but even the most expensive battery won’t perform or last very long if it is not charged correctly.

To ensure you get the expected performance and value for money from your batteries, make sure you refer to the battery manufacturers’ data sheet and check out our dual battery selector to find the best battery charging solution to help make sure you stay in charge.

To watch the full episode, go here

Looking to start your 4x4, camper trailer or caravan upgrade but not sure what products will allow you to travel the way you want? Take the REDARC Hilux product tour to find out what products are best for your power management and towing needs.