At the heart of every modern caravan and motorhome is an array of gadgets and accessories that survive off 240V power. And for those who want to avoid the crowds and save money by getting off the grid, but still want to run a microwave, lights and other creature comforts, need to have a good understanding of battery power and how to keep them optimally charged.
With so many different types of batteries, such as lithium, AGM, Gel flooded and calcium being common, it is critical to know which battery size and type are best suited for your needs and what the best system is to charge it.
This is your ultimate guide to off-road battery selection.
Lead Acid Battery Types
In the RV market, there are two main types of lead-acid batteries used, starting and deep cycle. The difference between the two is straight forward. Start batteries are like a sprinter - quick off the block and use a large amount of energy for a short time. They can provide a large burst of current for a short time to power your starter motor to turn your engine over.
Deep cycle batteries are like marathon runners that are designed to handle a lower energy demand for longer periods of time. A deep cycle battery is designed to be regularly discharged then recharged again. In a battery, one discharge plus one recharge equals one cycle.
The physical difference between a starter and deep cycle battery is that a deep cycle has thicker plates to handle deeper discharges, different grid patterns to improve current flow, higher density paste to increase cycle life and use different grid compositions depending on their type to maximise their life.
Selecting a battery for your needs
When choosing a suitable deep cycle battery, many consumers focus on the size, price, weight and capacity of the product, without taking into consideration where the battery is to be installed in the application.
But battery placement can play a big part in your selection, such as
- Near sensitive electronics – use an AGM/Gel, SMF (Sealed Maintenance Free) flooded. Avoid using maintainable batteries as the higher gassing rates can corrode and damage the electrics in the application
- In confined spaces – AGM/Gel, SMF (Sealed Maintenance Free) flooded battery Avoid using a maintainable battery as checking the fluid levels can be difficult
- Under seats and sleeping areas – AGM/Gel, SMF (Sealed Maintenance Free) flooded battery. Besides being inflammable, hydrogen and oxygen gas produced from maintainable batteries can be damaging to your lungs and respiratory system when inhaled
- When fitted under the bonnet of the tug – it is recommended that a maintainable/SMF flooded or specific AGM under-bonnet battery is fitted. If using an AGM make sure it is fitted with a plastic case due to the risk of the release of water-vapour from the battery.
Matching charging settings with the battery
Charging Current (Amps)
In all cases, regardless of battery type, you should check the battery manufacturer’s recommended maximum charging current (1st or “Boost” charge stage) and choose a charger with a rating the same as or below (but not above) the battery manufacturer’s recommendation.
As a general guide, most lead type batteries below the 180-200AH range typically have a recommended maximum charging current below 40A, so a smaller charger such as 25A would be the better choice.
Charging Voltage (Volts)
In all cases, regardless of battery type, you should check the battery manufacturer’s recommended maximum charging voltage (2nd or “Absorption” charge stage) and choose a charing profile with a maximum voltage the same as or below the battery manufacturer’s recommendation.
As a general guide, recommended maximum charging voltages for most AGM or Gel batteries are around 14.6V, flooded batteries 15V, and Calcium 15.3V, but always check the manufacturer’s recommendation. These points should be considered:
Float Voltage (Volts)
Once a battery is fully charged, to avoid overcharging and to extend battery life, the charger should drop to a lower voltage. Most manufacturers of high-quality batteries suggest a (float or 3rd stage) voltage around 13.3V for lead type batteries.
In all cases, regardless of battery type, when choosing a battery that must be charged in a high-temperature environment, such as engine bay, you should check the battery manufacturer’s recommended maximum charging temperature, as some batteries are not suitable for engine bay installations. In fact, some battery warranties are void if installed in engine bay temperatures.
Voltage settings are specified at 25-degrees
When choosing a battery charging profile, it is important to recognise that battery manufacturer recommendations are usually for a battery at 25C. For batteries in higher temperature environments, such as in an engine bay, it is recommended to charge to a lower maximum voltage, and in hotter climates, the lowest setting is generally advisable
- If the charging voltage is too high for the battery type, you risk overcharging the battery
- If the charging voltage is too low for the battery type, you risk undercharging the battery
- The absorption and float charging voltages play a key part in battery life and performance.
Battery Charging and Time
- It generally takes 40% of the total charging time to recharge the last 20% of a battery, this is the most important stage to help improve the battery’s service life and overall performance
- Using a fast battery charger with pre-set absorption times on smart chargers may not provide enough time to fully charge the battery
The importance of battery specification
Far too often we receive calls from customers who have issues relating to their battery or charger. All too often the solution lies in the fact that the user has ignored the battery specifications. These specifications are critical in ensuring what product should be used to charge and maintain your auxiliary battery.
The most relevant specifications when selecting a dual battery charger for a specific battery are the battery type (LiFeP04 and AGM for example), the maximum charge voltage and the maximum charge current.
Different types of batteries will have different chemical reactions when being charged so they generally need to be charged in a specific way. The charge profile will consist of a maximum charge voltage and will provide the battery current in the correct way to ensure it charges to a 100% state of charge.
If you pick the wrong charger or match it with the wrong profile you can expect to drastically reduce the batteries health and life, there is also a chance that the battery could fail. A handy dual battery selector tool can help get you started.
Today’s modern vehicles feature smart alternators, that are designed to improve fuel efficiency and reduce engine emissions. Vehicles equipped with a smart alternator allow the vehicle to control the output voltage from the alternator based on vehicle operating conditions, to reduce the electrical and mechanical loads.
A smart alternator does not consider the secondary battery’s state of charge, chemistry type or location in the vehicle, which are all influencing variables in how it functions, being tailored for the vehicle start battery.
Good DC-DC battery chargers such as our BCDC range are designed for both standard and variable voltage/smart alternators. They provide a tailored multi-stage charge process to the specific battery chemistry type regardless of where it is installed in the vehicle. Another useful feature is a solar input which gives the power to stay that extra day. A bonus is that it places less load on the alternator when the engine is running.
What are the best ways to maximise your battery?
There are several things you can do to ensure the longevity of your battery;
- Ensure your battery charger accepts solar charging, allowing less load on your vehicle’s alternator
- Monitor the battery voltage and stage of charge, preventing excessive discharge. Our 52mm Voltage gauges or Hummingbird RF Battery Monitors are perfect for this application
- Take the time to understand the design of your battery system
- Ensure your battery charger’s profile is suitable for your battery chemistry.
At the end of the day, selecting the right auxiliary battery comes down to you, your budget and how you’re hoping to travel. The most important thing is that you know before you get started what is going to work best for you and why, to get the best bang for your buck.