May 28, 2018

Choosing the best vehicle battery charger

In the last blog, we covered the things you should consider for your dual battery setup in your vehicle such as the type of vehicle you’re driving, the type of alternator you have, the electrical accessories you want to run from the electrical system and the length time spent free camping.

In this blog, we’ll delve a bit deeper into why these factors are important as it will decide on the best dual battery system you need for your set-up. The two main types of battery chargers on the market are Smart Battery Isolators and Dual Battery Chargers.


Smart Battery Isolators


Smart Battery Isolators have been used for a number of years and is 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 recognize 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 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.



This type of set-up 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 set-up 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, an In-vehicle Battery Charger is going to offer more flexibility for your dual battery set-up, 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 auxiliary battery is that a majority of vehicle alternators after 2010 do not put out more than about 14V after driving the vehicle for 10 – 25 minutes. Deep cycle batteries, which is what you would use for the secondary battery generally require charging at higher voltages, with the result being the battery will be undercharged from the alternator alone.

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 finer end of the scale, you would be better off supplying high octane fuel to a performance petrol engine.


BCDC In-vehicle battery charger 


Therefore, a DC-DC battery charger is recommended as it is designed to effectively charge an auxiliary battery to 100%, ensuring the prolonged life of your auxiliary battery. An In-vehicle battery charger achieves this by applying the correct voltage level to achieve a full state of charge and controlling the amount of current flowing into the battery so that it doesn’t charge too quickly which can otherwise cause 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 the bonnet as a dc-dc battery charger can overcome voltage drop from long distances. This 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.


Finding the correct size dual battery charger


If you are ohhing and uming going down the DC-DC charger route, then also consider the amps required. Dual Battery Chargers, typically range from 6 – 40 amps. So, 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 has a range of impacts but the worst impact is 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 then select the right sized dual battery charger, otherwise, you will just be wasting energy and possibly money.


A word on solar


Finally, let's 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 provides the added benefit of providing less load on your vehicle’s alternator. This 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.

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 works with a range of battery types including lithium iron phosphate batteries.

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


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 calculator to select your battery charging solution to make sure you stay in charge.


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