wiring a 2nd battery

Thanks Rus,
Did you install it yourself and if so did you connect the positive lead to the positive on your main battery or did you go the positive terminal on the alternator.
Steve

Steve, it's wired battery to battery for the positive and the second battery earth bolts on to any part of the motor. There are often spare bolts that a 12mm spanner fits somewhere suitable.

The advantage of the solenoid system, apart from not having to lift the bonnet, is that the main battery is kept ready for starting and only until the main battery is charged back up again after starting does the solenoid click in and allow the second batt to charge. Also if in the event of ,say, leaving your headlights on and flattening the main batt, then you have the ability to override the solenoid and use it to start the vehicle. Rus.

Leroy, you seem to have a misunderstanding of the words "solenoid" and "relay".
A relay is a device with electrical contacts which are activated by an electromagnetic force. It is used to switch current, like a remote operated switch. Bigger (often multi pole) type relays are called "contactor".

A solenoid is a device that performs some mechanical function by the application of an electromagnetic force. An example would be a fuel valve or the solenoid that locks or unlocks the doors, etc.

You can get relays with quite high amperage contact ratings, suitable for switching 12V but there are also others which are suitable to switch only AC voltages and many other varieties. One has to select the right relay.

The high current carrying capacity you mention is in most cases a myth. It will only come into play when the aux. battery is flat AND you wire it up with welding cables to the main battery, i.e you plan to start the car from the aux battery as well.
If the aux battery is there just to run a fridge, etc. then cables capable of passing 50A or so for a short time are adequate. 50A is plenty to charge the battery and it will drop quickly anyway as the battery takes up charge.

I made a compromise with my battery set up, as there is no room for a second battery under the bonnet it was fitted in a special box behind the drivers seat. If I do need this battery to start the engine ( happened only twice so far) I have made up longer jumper leads ( welding cable & clamps) which can temporarily connect the aux battery to the main battery to start her up. Being not fixed these cables also can start other cars or be used for welding, IMO a better use for additional heavy duty cables.

Troopie,

I think you felt like posting for the sake of posting to make a play on the words rely and solenoid. Generally a the term relay is used for low current applications and as such is not suitable for the intended application.
You contradicted yourself by saying on one hand the 'high current carring capacity is a myth' then go on to say 'it does come into play when the aux. battery is flat'. It's either a myth or it's not!! Here is an application where relay is not suitable.
Now I specified a solenoid because in the world of battery isolation it is common knowledge that the simplest form. Check out this link link text. You can use them for charging the battery but also you could use it for discharging. ie if your starter batt was flat you can bridge the solenoid to jump start yourself!
Hence the need for cables the same size as the battery cables as your starter battery so you can perform the jump starting task. For the sake of $15-20 bucks I wouldn't scimp on cable. So you can see why a simple relay is not suitable.
Contactors are used for high AC current and voltage applications and are not suitable at all.
I'm glad you're happy with your battery setup but I prefer to have one that is a little more robust.

Leroy

So Troopy, I hope the battery you've got behind the seat is one of those gell type. You know, the ones that won't spill acid all over you in the event of a rollover !!!!!!!!!! Rus.