Surely the space is adequately ventilated, particularly when the vehicle is in use.
Half the air that comes in the front of the vehicle by way of the ac system is going out thro each of the rear quarter compartments.
I'll look into it further but on the face of it I can't honestly see a problem.

I think if you put a battery as per Dans method you will be fine with venting.

I think this as within a few inches you have a vent DRAWING air out of the cabin as you drive along.

If you could get another 110ah Bosch or varta in there then that would be perfect as it would be better to stick the new one up front and the old one at the back after giving it a good clean!!  FFRR MY06 facelift With TDV8 Alloys Zeros/ATR's
Mantec Sump Guard, Rigid Load liner, MY10 BT upgrade.

venting wouldn't be too much of a hassle with most "sealed" batteries, many have a vent plug on the top which you can route a little pipe upto the vent that is about 3" higher.

Just thinking out loud, but does any one have a wiring diagram for the battery terminals and charging circuit?

Regards, Luke

Last edited by barracuda816 on 25th Jan 2013 7:45pm. Edited 1 time in total

The main three problems i see with Dans system are:

1: parasitic losses, the weakest battery will draw from the good one.

2: over charging the strongest battery, as the alternator will keep charging the weakest battery after the strongest has allready charged, reducing battery life.

3: This is the biggest one for me, there is no redundancy, if you run the batteries low (say with a camping fridge and some lighting when camping) then you will still need a jump.

OK, I'll take your points one at a time.

barracuda816 wrote:

1: parasitic losses, the weakest battery will draw from the good one.

barracuda816 wrote:

2: over charging the strongest battery, as the alternator will keep charging the weakest battery after the strongest has allready charged, reducing battery life.

barracuda816 wrote:

3: This is the biggest one for me, there is no redundancy, if you run the batteries low (say with a camping fridge and some lighting when camping) then you will still need a jump.

Probably true, but to run down 2 batteries with AGM technology will be a fairly impressive feat. As I said before, if you manage to flatten 165 ah of Gel technology you either need to get some alzheimers tablets and stop forgetting what you've left on, or you need a bigger car. Perhaps consider one of those Alde trailers with a load of batteries in.

@barracuda816

Reading thro this post, I don't understand why a proven system of two batteries separated by a heavy duty relay switched by the ignition circuit from the primary vehicle battery is so unsuitable for your needs.
It would provide everything you require, ie the ability to use current comsuming equipment to the point the secondary battery would be discharged whilst leaving the primary battery fully charged for vehicle starting when required.
I've installed this arrangement on a number of vehicles in the past without any problems whatsoever as have many thousands of caravaners. Not everybody bothers with split charge circuits.
One point I would take issue with is your proposed 500A relay, this is quite frankly absurd, there is no possibility whatsoever of anything like that current flowing between the two batteries when the connecting relay is closed, indeed in the past I have used 30A relays for the exact same purpose without problems.
If you are not confident of using a 30A relay use the Durite 100A unit I posted earlier, even that is over-kill.
Installing a second battery in the rear of your vehicle is simple, the secondary +ve battery lead connected to the existing 100A cable, the -ve battery lead connected to earth. The spliting relay can be fitted in either +ve or -ve cable at your preference, with the coil switched from a local ignition controlled feed of which their are two at the rear of the car.
You appear to be worrying un-necessarily over trivia.
I would just get on and install the simplest option as above and enjoy your RSE to the full.

Installing a second battery to the car connecting into the existing 100A cable is simply a means of increasing the Ah capacity on the car and is totally unsuitable for your described future use.

It may interest you to know that for the past 5 months I have had an additional battery, 110Ah Varta, sitting in the boot of my car connected to the vehicle by way of a plug into the load space accessory socket, with a 10A fuse in the plug.
The accessory sockets in my car are live all the time.
I have had no problems, the second battery has been kept fully charged by the alternator and I benefit from having a combined battery capacity of 220Ah on the car.
In my opinion this is what LR should have been providing in the first place.
Come warmer weather I will make the arrangement permanent by way of the existing 100A cable, hopefully with the present additional battery but if not something close in terms of capacity.

Last edited by nicedayforit on 25th Jan 2013 10:46pm. Edited 1 time in total

mzplcg wrote:

Perhaps consider one of those Alde trailers with a load of batteries in.

Now there is an idea!

I take your point on issue one, as long as both are the same type it should be minimal, and as it will be driven almost daily its a non issue i suppose. I didnt know they would effectively see-saw though it makes sense when you look at it.

point 2, i Dont know why i thought that, (i do know it wouldnt overcharge at 14.2ish, honest ) i blame a brain fart.

Point 3, I agree under normal use, 160ah would probably be sufficient. But for even weekend camping it would be easy to run them below 50% dod.

The main thing with my idea is i "should" never be unable to start the engine.

I will probably run the simple parallel set up due to cost, but when i have the readies i may try the below set up (again please excuse the poor diagram, its just to give an overview)

With the disengaging/engaging of the batteries do you think it would suffer from transient voltage spikes?



Uploaded with ImageShack.us

Plus with this it would be extreamly easy to add further dedicated batteries (a winch batt ect)

@ nicedayforit

I understand what you are saying, but if i where to add a second battery the standard relay way, the main (starter battery) would still be connected to all the on board computers, RSE , FBH ect. And the 8awg wire running to the second battery will not be anywhere near man enough to carry the required current to start the engine.

So the only option as i see it (without running larger cable) is to disconnect the main battery, run everything off the second battery until i want to start the engine, that is why i need a larger relay, as i believe the starter motor itself will consume around 200amps (i haven't measured this yet) all-be it for a short period of time, it would still have to be continuous duty for the coil side.

Saying all this, i fear you are right about being overly concerned with the trivia.

And after looking at it and getting all the input that i have, i have come to the conclusion it would be cheaper and easier to run some decent cabling to the rear and do it the conventional way.

"I understand what you are saying, but if i where to add a second battery the standard relay way, the main (starter battery) would still be connected to all the on board computers, RSE , FBH ect. And the 8awg wire running to the second battery will not be anywhere near man enough to carry the required current to start the engine."


Not if you have the ignition off.
When you turn the ignition on to start the car, the starter will operate from the primary battery even though the relay will close at the same time.
Trust me, it works.

"So the only option as i see it (without running larger cable) is to disconnect the main battery, run everything off the second battery until i want to start the engine, that is why i need a larger relay, as i believe the starter motor itself will consume around 200amps (i haven't measured this yet) all-be it for a short period of time, it would still have to be continuous duty for the coil side."


You disconnect the primary battery from the secondary battery when you turn the ignition key off leaving you to run your equipment from the secondary battery.
You don't need a larger relay, the current is nothing like you imagine.
The relay coil is taking milliamps when energised.

Saying all this, i fear you are right about being overly concerned with the trivia.

"And after looking at it and getting all the input that i have, i have come to the conclusion it would be cheaper and easier to run some decent cabling to the rear and do it the conventional way."


You don't need to run "decent cabling" to the rear, the existing 100A cable is adequate for your purposes.


Just to clarify, if you fit a second battery in the rear as described above you would need to connect all the equipment you wish to run off it even if this means disconnecting items from the present battery circuits.
I usually fit an additional fuse board to the second battery to serve the various items.

Nicedayforit, i think Barracuda is talking about disconnecting the earth cable from the main battery to isolate it therefore he will need a high capacity relay to take the current draw from the starter motor. the way you are suggesting is the same as me i think. using a smaller relay to disconnect the + on both batteries when the ignition is off. the relay is only used for charging then and not starting. i am pretty sure there are just two + cables at the main battery, one for the starter and the other for supplying everything else. now all you would have to do is put the relay between the main battery + terminal and this cable for supplying everything else and have it switched with your ignition. this would then isloate the main/starter battery from the rear one with the ignition off and join them for charging with the ignition on. Barracuda, the way you are suggesting will work but i think this way is by far the cheapest and the end result will be the same. also for a rear battery you would prob be better using a deep cycle battery as these are designed to be discharged and recharged a lot where as the starter batteries are not and wont last very long. '04 td6 se
'63 land rover s2 200tdi
'04 mk indy kitcar bike engine

wats39,

If that is right with the two wires on the main battery terminal, that would indeed simplify things. does anyone know if i can get hold of the wiring diagrams i could confirm if there is anywhere the voltage could feed back down the line, i.e the charging circuit.

Regards, Luke

Send me your email address by pm Luke and I will send you the vehicle wiring diagrams.

Barracuda, will try get time tomorrow and have a look at mine to see if there is just the 2 wires that i think there is. a wiring diagram would be ideal but you dont seem to get them for any vehicles these days. prob to do with the amount of wiring in them now  '04 td6 se
'63 land rover s2 200tdi
'04 mk indy kitcar bike engine

I stand corrected. where did you get the wiring diagrams from Nicedayforit? '04 td6 se
'63 land rover s2 200tdi
'04 mk indy kitcar bike engine

Can't remember but if you pm me your email you are quite welcome to a copy.
By the way you are correct 2, 35mm2 cables off battery +ve terminal.