dual battery system.

For my trip through Africa I used a mechanical system, which basically is an extra lead from your primary battery to your 2nd. I then used a heavy circuit breaker key (http://cgi.ebay.co.uk/Battery-Isolator-Cut-Off-Key-Switch-FREE-POST_W0QQ...) installed next to the ignition switch. The key can only be removed with the 2nd disconnected, so you can not drain your main battery. On trips like these I prefer simple, and you can not get simpler than this. I have been stuck with a very expensive device before and then Chris from Boab gave me this idea. They do this for all their serious off road trips.

Depends if you have connected them in "series" or in "parallel"

If they are connected in parallell, negative to negative and positive to positive, the same way you would jump start a car. Then the voltage remains at 12v but you have doubled the amperage.

If you connect them in series, positive to negative then you have doubled the voltage output but the amperage remains the same.

I used to fancy my physics teacher, she had a Triumph Stag.

You have it 100%
That is why it is my preferred way of doing it. It is cheap, simple, and nothing can go wrong.

hi g,

there are a number of systems available and i think i've tried most of them (national luna, ibs, piranah and a simple vsr solution to name them all - on different cars of course).

the simplest system (which is also the one i have adopted on my pinz by the way) is as follows:

intal the aux battery and link it to your main battery in PARALLEL (i.e. positive to positive and your negative gets earthed onto the chassis) via a VSR (voltage sensitive relay). Basically, the voltage sensitive relay lets charge flow to your aux battery at a predetermined voltage (normally about 13.7V) and cuts out below a certain voltage (about 12.5Volts). The key is to buy a good quality VSR: this is the simplest 'dual battery' set up and is bombproof. no monitors, no displays (except an LED on the VSR to indicate it is 'working/charging'), no fancy electrics...beautifully basic and very functional.

you can buy decent quality VSRs (Voltage Sensitive Relay) from good Marine Electronics Shops: the best ones happen to be made in New Zealand (the name currently escapes me!). if you're going to instal a dual battery set up, you might want to run the winch off of your auxiliary battery as well. Some people do, others don't: the simple fact is that it doesn't matter if you choose to go the VSR route as you can buy decent VSRs where you can manually 'link' the batteries if you ever need to in an emergency. For this reason alone, I opted for a Marine VSR (because it is waterproof - you never know....), it was rated to up to 300Amps (i.e. you can run a winch/starter motor no problems) and it has a manual 'link' switch on it (in other words if your primary battery is completely flat you don't need power to the unit in order to switch it). to answer your q, you do not have to go back to the alternator at all: effectively by using a VSR your aux battery gets the same charge as your primary one - the voltage is already regulated by your cars voltage regulator which charges the primary battery. Like i said, this is the simplest 'system'.

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Alternatively, if you only want the second battery for your fridge, you can buy a national luna extra battery pack. this is basically a box which contains your aux battery and the electronics as per their in-vehicle dual battery charging system. this is a good solution as you can easily take it out and put it either in your tent to also run lights off of or store it in your garage when you're not using it. you can also buy monitors for it if you want to go that route. the only problem with it is that it is quite bulky and therefore a bit cumbersome to move around. it really depends how much room you've got in your car. Also you can only 'link' the two batteries up to about 100 amps - so you can't start your car off your aux in case your primary battery drains (after a winching exercise for example - your winch runs off of your primary - and you stall........it can happen....you're pretty much stuck if you don't have another car nearby to connect jump leads to)

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Lastly, if you do want to go for an in-car set-up, the best by far that i've used and have experience with is the ibs system. it is the simplest, easiest to use/read and the link option rating allows you to start on the auxiliary battery if your primary is down. what makes it better than the other two ones that i've used is that it is much easier to incorporate a solar panel into it if you want to trickle charge your batteries (to run a fridge for example when it is very hot in the car for a day or two). If you don't want to go the solar route, i suppose it probably wouldn't make a lot of difference between the others (i've only used national luna and piranah ones) in terms of function: i found they all work basically the same way and they all performed their tasks satisfactorily.

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the above is a lot of info to digest, but i would really urge you to think exactly what you want your set up to do before going out and buying one: they are not all the same and they don't all do the same thing. dual charge systems are expensive pieces of kit to fit (not necessarily to buy). they take a long time to install and can be quite fiddly. if you don't like what you've bought and installed, ripping it out and replacing it is usually not really an option as they are a pig to take out and a pig to reinstal another one in its place. if you want any more info, pm me and i'd by glad to try to help you.

ph

where are you finding the room to mount 2nd batteries?

LEEU. Yes, that makes a lot of sense. As I mentioned, having tried all the fancy systems - and having small kids - I also went back to the basics (i.e. the VSR route). If I ever prep another exped car, I will give your idea a try - as then I will only be able to blame myself for not disconnecting the isolator switch (I'm assuming that my kids will be a lot older!). ph

Ah cheers, for a big wagen the G is a bit sort on space!

yes. to make sure, give the guys a call (I've found them very helpful in the past - and they don't mind that one asks VERY amateur questions about how to wire up simple switches, etc, etc). they will also ship to you in belgium by the way. good luck/ph