If you’re into any sort of serious off-roading, chances are you’re going to want to add lots of accessories to your vehicle, both to get you out of trouble, and to give you more comfort when you’re far from the madding crowd.
These can range from fridges to winches, extra lights to invertors, towing connections to televisions. Whatever you choose, they all have one thing in common – they run off your vehicle’s battery, or if you’re clever, batteries!
For most of us, batteries are big amorphous oblong plastic boxes usually found under the bonnet.
They connect to the vehicle’s electrical system via clamps on two big lead posts set into the battery surfaces, and the handbook tells us we must ensure these connections don’t work loose, or get gunged up with muck and green mouldy-looking stuff caused by oxidation of the lead.
Some batteries have a line of screw tops on the upper surface, and we’re also told we must regularly unscrew these and check to ensure the liquid inside (it’s a mixture of distilled water and battery (sulphuric) acid is above the level of the plates inside.
However, these days most batteries come completely sealed, so maintenance of these is limited to just ensuring the connectors don’t get mucky. And many connectors come with a plastic cover ensured to prevent this, too.
So on the whole, a modern battery, as fitted to your vehicle when you get it, requires very little care and attention – which is why we mustn’t forget about it!
First up, we must take care it doesn’t run completely flat, because every time you do that it lops a bit off the battery’s life.
The ordinary battery fitted to your vehicle as standard – let’s call it the “starting battery” - is designed to cater for the car’s everyday needs, and definitely NOT all the additional extras we’ve mentioned above, so if you use it for, say, running your camping fridge, and leave the fridge on until the battery has lost all its juice, first of all you’re going to need either a jump start or other assistance to start your 4WD, and secondly you’ve dramatically shortened the life of the battery in terms of its ordinary everyday activities.
Yes, we all know a car needs a big amount of electricity from the battery to start it in the first place, and once the engine is running that electricity is replaced by the alternator.
Other calls on the battery, such as electric windows, ventilation fan, and your sound system are also usually operated while the engine is running, and if not, are activities which don’t use a lot of power anyway.
However, running your fridge, the TV, and so on requires energy to be expended over a much longer period
To cater for this, batteries are designed for different tasks, and using a battery for a task for which it is not designed can lead to its early death.
Generally speaking a “starting battery” for a 4WD will have a sturdier construction and a higher CCA rating than, for instance, that in your run-of-the-mill econohatch.
CCA rating is an acronym for “cold cranking amps”, which simply put, means the amount of “grunt” it has to start your vehicle’s engine. A heavy duty 4x4 battery will have a CCA in the early 600s, so you can easily start a big turbo-diesel on a cold wintry morning.
Another measurement often bandied about is RC – reserve capacity. This measures how long the battery will operate essential accessories if the alternator fails or the engine isn’t running.
A heavy duty 4x4 battery will have an RC of upwards of 130 minutes. The bigger this number, the longer you can drive with a broken alternator or alternator belt.
A third measurement quoted is “amp hours (AH)”, which is a measurement of how much current is available for “X” number of hours under standard test conditions before the battery voltage drops. A typical battery for a big automatic car or 4WD is 55 AH.
That’s the “main” battery, designed to start the engine and keep all the usual bits working. But what about those other bits – the fridge, the camp lights, the TV set?
These put entirely different demands on your battery, and so require a different type.
The fridge and other accessories you may use for camping require relatively small amounts of power, but delivered over a long period between recharging, while winches may require lots of power, from a few seconds to an hour or more.
For this sort of treatment you require a deep cycle battery, and it’s totally different to the one you use to start your 4WD’s engine.
They are capable of holding more power than an ordinary battery, and they can let it out slowly, and in addition they don’t mind if they are run almost flat on the way.
However, just as they let the power out slowly so they like to get it back slowly, and recharging can take a long time – usually longer than you’re going to be driving your 4WD. This means they often have to be recharged once you get home, or even on your trip if you can get access to mains power.
Deep cycle batteries are rated in amp hours. Around 65 AH or more would be required for typical camping use.
A battery should not be discharged at a higher current draw, or asked to deliver more amps, than its amp/hour rating divided by 10 in order to get maximum capacity out of it. In the case of a 65 amp/hour battery that would mean it should not be asked to deliver more than about 6.5 amps for best service.
A typical 28 litres cooler/warmer fridge cooling down to -1 degree would pull about 2.5 amps.
Winching requires a slightly different approach, as under full load conditions the winch will typically draw around 450 amps, which will quickly suck the life out of an ordinary “starting” battery.
So what the aficionados do (and what we did on our Project Re-a-Range) is to connect the two batteries in parallel, with a solenoid energized by the winch, giving the extra reserves necessary for winching.
In this case a deep cycle battery with a large CCA rating (600 amps) was chosen – sometimes this is known as a “hybrid” battery as it combines the ability to crank out huge power but doesn’t mind being flattened!
A voltage sensitive relay module is
fitted to ensure that when the deep cycle battery is being used for camping purposes any current draw will not flatten the starting battery. .: