Hi guys,

I have a RSE system in my vogue se, and would love to be able to actually use it and maybe the parking heater with out the fear of being stranded.

Now, i know its easy enough to fit a second battery in the boot, and wire it the the 8awg supply in the right electronics cubby. And that will give me more capacity, but doesn't ensure i wont be stranded.

Im inherently lazy and a bit of a cheap skate, so running some 4awg cable and setting up a big fancy split charge and isolation system is out of the question for me.

So i thought what about a heavy duty solenoid (similar to this http://www.texasindustrialelectric.com/relays_1119865CD.asp ) wired in series with the negative main battery terminal. Have the exciter wired to an ignition live, the second battery wired in as normal.

This uses the second battery as its sole power supply until you put the ignition on.


Then, in case you completely flatten the second battery, and cant put the ignition on, have a little 12v battery (or two 9v would probably be fine) in the glove box ready to fit to an emergency point the the solenoid,to bring the main batt back on line.

This is the cheapest, simplest most fool proof way i can think of.

Please feel free to pick this apart. I appreciate the feedback.

Regards, Luke

edited to change the solinoid link

Last edited by barracuda816 on 24th Jan 2013 10:08pm. Edited 2 times in total

The only fly I can see in that wee pot of ointment is this. If you actually do flatten the second battery, where does the +12v come from to fire the solenoid?

Plus of course, finding a constant duty solenoid of that rating is no mean feat. I've never seen one TBH.

EDIT. One other thing. Assuming you can overcome problem 1, when you do fire the solenoid there is going to be an inrush current between the 2 batteries which will pop the 100a fuse to the rear.

Mostly nothing wrong with what you are proposing. A lot of people have done the same to other vehicles in the past, me included.
Not quite as sophisticated as a split charge system, but perfectly adequate.
This relay is what you want, fitted in the earth lead of your SECOND BATTERY. If you switch the relay from the primary battery you shouldn't need to worry about additional back-up batteries, unless you need to sit with the ignition on for any reason.
You need 16mm2 cable to connect to the vehicle wiring and earth cable.
You shouldn't need a fuse in the +ve connection cable, the circuit is already fused at 100A.
Would be a good idea to connect to the second battery terminals using quick release connectors.

htttp://www.ebay.co.uk/itm/Durite-12v-Heav...35bafa8a83

Last edited by nicedayforit on 24th Jan 2013 10:03pm. Edited 1 time in total

Erm NDFI, I reckon you missed the point. Read the OP again. He wants to put the relay in the earth of the MAIN battery. So if the 2nd one is flattened the starter battery is still good.

Yes you are right. I shall edit.

Problem one will be overcome by the 2x9v batteries, once that is on and the engine has started just unplug the little 18v pack and stick it back in the glovebox.

That is a good point ref problem 2, im not sure how much a dead sla battery would pull. some testing would be in order, but the cb i want to fit is a auto resett bussmann 50amp (allows 130% for 30 seconds, and more % = less time).

regards, Luke

When i changed the battery on mine iirc there were 2 positive red cables. 1 that went to the jumper post then looked like it went straight to the starter and the other with the explosive charge on it into the inside behind the fusebox area. could you not disconnect the explosive charge cable and fit a relay between it and the battery and have the relay switched with the alternator when the engine starts. this would then keep the front battery for starting only and the battery in the rear for powering the rest of the vehicle and when the engine starts, both batteries will charge. '04 td6 se
'63 land rover s2 200tdi
'04 mk indy kitcar bike engine

Excuse the very poor, very basic (extremly quick using paint) wiring diagram.

Hopefully this will help explain it a little better.



Uploaded with ImageShack.us

Dont see why your idea wont work. what you will have to do though is fit a diode on the +12v ignition feed to the relay though or when you connect your 18v back up batteries it will put 18v through the rest of your ignition circuit. either that or disconnect the + wire to the solenoid before connecting your back up batteries. have you priced one of those relays? doesn't look like it would be cheap. '04 td6 se
'63 land rover s2 200tdi
'04 mk indy kitcar bike engine

To be honest I haven't priced the continuous duty contactors. I am going to try and do that today.

I have massively over complicated the failsafe. Instead of the small Emg batt, it would be easier to run a bypass switch for the contactor ( like the cut off switches you get of rally cars) then if the second battery goes flat it's just engage bypass and all is good.

Thanks for all the feedback so far guys.

You know what.....here's a better idea. What you need is capacity TBH. You'd have to live in the car watching TV for a week to flatten this.

replace the MAIN battery with this
http://www.tayna.co.uk/H15-Varta-Start-Sto...P8824.html

AGM technology (Gel to you and me) dsigned for STOP/START technology - i.e. Deep Cycle.

Then in the space at the back fit one of these
http://www.tayna.co.uk/LFD60-Varta-Profess...P3635.html

That gives you another 60aH meaning a total of 165 ah and 920 cold cranking amps.

If you manage to flatten that lot then you need a different car.

What about all this stuff in relation to toxic fumes? If the battery has a breather, can one poke it into the air con vent?

I was having a good poke about on the tanya site last night, proper sealed batteries (e.g. Optima Yellow top) are b y expensive!

Also, what is wrong (if anything) with what dan_uk_1984 did, which was to simply wire in a second battery in the boot? .
Experience is the only genuine knowledge, but as time passes, I have forgotten more than I can remember
Volvo V70 P2 2006 2.4 Petrol 170bhp Estate SE
MG Midget Mk1 1962

Previous: L322 Range Rover TDV8 3.6 2008; L322 Range Rover TD6 3.0 2002; P38A Range Rover V8 1999

To be honest 165 ah isn't that hard to drain to a point where it won't start the td6. But unless I find a cheaper solenoid ( the cheapest I am comfortable fitting is £130 I will just go with the twin batts and a cb.

However, I am concerned about the weakest battery draining the other, as they won't be balanced/ matched.

Regards, Luke

Having roughly measured the space in the rear for a second battery I think it is a possibility that the standard 110A Bosch / Varta battery could be persuaded to fit.
I intend to have a closer, more detailed, look when the weather gets warmer.

You need a properly sealed battery in the passenger compartment - Bosch/Varta aren't. You could vent them somehow, but it's going to be hassle.

Frustrating as I have a spare Bosch 110

I have twin Optima Yellows on my Jeep - they are wired in parallel - both earthed and a 100a relay across the positives powered by ignition live. (Worst case I will use my jump leads) the guy from XEng where I got the relay from reckons 200a is a reasonably high frequency switching rating, but for continuous use, the relay would easily handle 200a