Deep cell batteries ?

BackTracks deep cycle batteries are designed to supply low currents over a long period and not at all suitable for starting vehicles.
Batteries fitted standard in vehicles are designed to supply high cranking amps for a short time and not at all suitable for use as a deep cycle battery.
You can see the range of batteries and full information available at Car and Deep Cycle Battery FAQ

thanks for the help guys . So I can use them.

Good news.

Craig
In my published books, magazine articles and responses to queries on websites, I try to provide answers that will work - not that may work. But there will often be exceptions that suit some people or some circumstances.

Re charging disparate batterises from a common source. There's no problem charging different capacity batteries of a similar type. Each draws whatever it requires.

There can be a problem when charging starter and deep cycle batteries in parallel however in that a starter battery is recharged (after starting an engine) in no more than two-three minutes - and will have 14.2-14.4 volts across it. This causes the voltage regulator to cut back the charge and hence the deep cycle batteries may take longer to charge than expected.

The Rotronics unit gets around this by charging the deep cycle battery (or auxiliary battery) separately, but as the alternator is limited to starting battery type output the second battery will not charge beyond 70%.

Re using deep cycle batteries for starting purposes. Given a big enough battery bank there's no problem. It's also less of a problem with a petrol engine as far less cranking current is required. If the engine is in really good shape and starts within a second or so then what you are doing is to 'pull the surface charge from the plates'.

But when that is exhausted (the time varies from battery to battery but is short) the very slow electro-chemical reaction between the limited plate surface area of a deep cycle battery and the electrolyte will reduce available current. As such batteries have high internal resistance, attempting to do so will generate a great deal of internal heat and plate damage will inevitably ensue.

There may also be problems starting at very low temperature as the available current is greately reduced.

Re battery longevity - Trojan batteries are likely to withstand this usage better than most - but I maintain that their life span in this usage will be less than for their intended use.

I feel that in matters such as this, it's interesting to hear of exceptions - but they are best seen as such.

I know that you are not recommending this, but there is a similar situation with the occasional posting to the effect that a second (isolated) battery is 'not necessary'. Perhaps not in some instances, and where a jump start can be relied upon, but suggesting this as a general principle is unfair to many readers who may act on the advice.

Whilst researching my book 'Motorhome Electrics' I contacted almost every leading battery maker worldwide for advice. There was general agreement on most matters and it was on that 'averaged advice' that I wrote that part of the book. Prior to publication, draft copies of the battery content were sent to about 20 of the companies - and all approved the copy. My responses on forums such as this reflect this.
Collyn Rivers

BackTracks,

Collyn is right (in fact he is a bloody guru on this subject ... buy his books!)

I managed to wreck two deep cycle batteries in less than 12 months each when connected across the typical alternator/ cranking battery via an ARB Isolator in my work Nissan. Went back to using a cranking battery for Aux use in this situation and they work fine and are much cheaper.

Deep cycle batteries only work well when they are charged the way they like it (which is exactly what your typical alternator does NOT do). Solar charge controllers or specialised alternator regulators or the Arrid chargers are the only ways that will work and give you many years of life from a deep cycle battery.

JohnS