Right, yet again I couldn't start the RR after 3 days not being started. Going to do more checks for a parasitic draw but in the interim I have decided to change the FSR as this seems to be what most recommend.

In addition I intend to fit a second battery with a split charge voltage sensing relay and hope that this will not allow the cranking battery voltage to drop to low to start the car.

Second battery fit out thread here: http://www.fullfatrr.com/forum/topic26065.html


Any advice on other areas to check or improve would be very welcome.

Fitting a second battery as per your link and using a voltage sensitive relay won't prevent your cranking battery discharging due to parasitic drain, all it will do is ensure your second battery doesn't drain when the ignition is off.
This is due to the fact that the front fuseboard, which serves most of the cars electrics is connected directly to the existing cranking battery at the cranking battery +ve terminal.
Your cranking battery will still drain due to parasitic drain unless you resolve the drain. You will however have a fully charged second battery, what use this will be to you if you can't start the car I'm not sure about.
I've looked in some detail at fitting a second battery to my own car purely for cranking purposes either using the existing vehicle battery or the second battery for purposes of cranking.
I've come to the conclusion this really isn't as easy as it first appears as to make it work you need a fully charged battery for cranking and at least a partially charged battery to operate the various circuits to start the car, something which appears to me to be impractical.
Having a dedicated cranking battery would involve extensive alterations to the vehicles' existing wiring something I'm not sure I would be willing to tackle on a RR.
I'm not even sure about the benefit of a voltage sensitive relay if you simply connect the second battery to the first at the rear fuseboard as shown in the link. This would only be of benefit if you intended to run equipment from the second battery whilst the engine was off. The arrangement is more suitable for a "leisure" battery set-up. It won't help you start the car.
Connecting the two batteries together without the voltage sensitive relay would almost be more beneficial insofar as you effectively double your battery capacity thereby any parasitic drain has a reduced affect.
This of course assumes that two batteries connected to each other in parallel don't start to discharge each other which can happen.
I haven't bothered with a second battery due to the above, instead I concentrated on finding the cause of my own initial parasitic drain and resolved it. Imo a more useful thing to spend time on.
If you do go ahead and create a cranking battery which is isolated from the vehicle electrics I would be grateful of you could provide a description of how you achieved it, I would be very interested.

I understand what you are saying and I agree completely. And I do intend to find the parasitic drain although last time I did this I could not find a drain, but I may have missed something.

My thoughts for the second battery are as follows. I will allways have a spare fully charged battery in the car, should I need it in an emergency ie flat main battery when I am away from home.

I have a set of jump leads that are long enough to go from the spare battery (after releasing the quick release clamps first), through the car and front passenger window and reach the jump points in the engine bay.

I am considering an Isolation switch to make it easier to disconnect the spare battery from the cars systems, before using it to jump start.

Does that make sense?

Yes that makes perfect sense, effectively you are ensuring that you always have a fully charged battery with you that you can use as a "battery pack" should the need arise due to a flat car battery.
The long jump leads is interesting, they will have to be substantial if you are to minimise voltage drop and ensure adequate current flow for starting. I'd been thinking along similar lines but simply having a spare 110AH battery in the boot in a battery box connected to the rear fuseboard connection and earth by way of Anderson connectors. My idea would be to simply manually disconnect the spare battery by way of the connectors and should the worst happen and I end up with a flat cranking battery, carry the spare battery to the front of the car and connect with jump leads. I would envisage this only being in exceptional circumstances and wouldn't propose to carry the second battery around routinely. This is why I have a second battery, battery box and Anderson connectors lying in the garage waiting for me to do something.
The obvious thing is to have a dedicated cranking battery available fully charged at all times but as above this really is not easy to achieve on a RR.
You could of course run a 35mm2 +ve battery cable from your second battery to the +ve jump post under the bonnet with a heavy duty manual isolator switch in it and do away with the need for jump leads altogether. Not a difficult job.

The jump leads I have are very heavy duty. I think they are from the haulage industry so easily up to the job.

I had thought of carrying the spare battery in the boot as and when, but decided to make it a permanent fixture because (a) I would forget to keep a charge in it (b) I can guarantee that when I need it, I will have left it in the garage (flat)

I will explore the idea of a direct connection between the +VE post and the +VE jump start point with an isolator. The problem I forsee is routing a cable of that size.

Thank you for the input, I appreciate it

Do you reckon two batteries (without the voltage sensitive relay) would discharge each other in ping pong fashion until they are both flat, or only in as much to equalise the charge between the two ? .
Experience is the only genuine knowledge, but as time passes, I have forgotten more than I can remember
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The only problem I could foresee is if the two batteries were in a different condition to each other eg one was older and not able to fully hold a charge to the level of the newer one. IMO it would be better to start with two new batteries and let them grow old gracefully together. Generally two batteries connected in parallel will be fine even batteries of different capacities.
Having a voltage sensitive relay fitted does mean you have a fully charged battery available on the car should the primary car battery discharge for what ever reason the problem is what you can do with it. The idea of using jump leads from it in an emergency to start the car is one use I just think it would be better if a more engineered solution to starting the car was available.

iphs wrote:

The jump leads I have are very heavy duty. I think they are from the haulage industry so easily up to the job.

I had thought of carrying the spare........................

Thank you Pete, I will take a look.