Member - Graham replied:

I had a similar situation with a work trailer, i installed a basic dual batt system as suggested by a auto sparky, a line from batt to a solinoid , solinoid wired to ign with a manual switch in car and use a circiut breaker instead of a fuse. cost at the time was about $50
Check with local auto sparky to re your vehicle, (electronics) mine was an early diesel. electronics were radios.

Member - Paul replied:

Hi Keith, I ran a 2nd battery in my camper trailer for 4 yrs & had no problem. I charged it via a 6mm cable direct from my cranking battery
in my pajero. this was isolated by a relay(soleniod) when the engine was not running. I used 50amp anderson plugs between the trailer & the car so I could connect & disconnect. this system is simple & reliable & I had no problem with my electronics (the pajero is full of them)
hope this helps. regards, Paul.

Nordave replied:

Keith. i am about to do this with my camper and would like to point out the following. (I am and electrician by the way.)
1 When a battery charges it gves off a flammable gas,hydrogen, this is
why you are always told not to check your battery levels with a match. Although in normal stuations this is not a lot of gas if the battery is in a cuboard etc it may cause an explosive situation.I am going to mount my extra battery in a ventilated box on the draw bar.
2 If you flatten the battery in the camper,when you run the engine a very large current will flow to the discharged battery. the normal 2.5 or 4mm cable that is in trailer plugs will not handle this and will melt and short. This Idea of having a seperate 50 amp plug is good but you will need more than 6mm wire to handle this . One solution may be to fit a circuit breaker to limt the current flow. I sugest you have a talk to an auto electrician to determane the amount of charging current etc available as this will vary with the set up of your electrical system and the size of your altenator.

Peter S replied:

The other thing to consider is that if you discharge your trailer battery alot, then the potentail of damage to both batteries is quite major.
The amount of current between the 2 when in connected together can cause heat up in both batteries. The uptake of this is is bending plates shorts and reducing life of batteries.

All this behind us what are you giong to connect ie Fridge lihts and all the goodies or a few lights.
If a fridge then
I would recomend a good quality battery isolater (not a straight soleniod)

If just a couple of lights then a regulated 40 watt solar panel will keep you going for quite a long time.

Member - Graham replied:

I had a similar situation with a work trailer, i installed a basic dual batt system as suggested by a auto sparky, a line from batt to a solinoid , solinoid wired to ign with a manual switch in car and use a circiut breaker instead of a fuse. cost at the time was about $50
Check with local auto sparky to re your vehicle, (electronics) mine was an early diesel. electronics were radios.

Member - Nigel replied:

I wouldn't recommend using the stardard trailer plug for charging as the voltage drop by the time it gets to the trailer battery will probably mean that you'll get no charge anyway.

I have starter cable running from my Rotronics controller to a 50 amp anderson plug next to the 7 pin trailer socket. This works well.

Another (more expensive) option is to get one of those regulated 12 volt chargers that run off 10+ volts - try www.12volt.com.au

Drew replied:

I have this setup in my trailer and was provided by local 4x4 company. Works extremely well using additional solenoid/isolator of some type and I have had no problems. It has Anderson plugs connecting and heavy wire running from the second battery. When camping I also trickle charge the camper battery using a solar panel (very small)

Axel + Karen replied:

Keith , is feasible, have used 7 pin plug for over 12mths no problem, is LARGE SIZE not small as normal used on car,, we use the rotronics w/ender system,, main bat isolated from 2nd bat as soon as engine off ,,,all acc run from 2nd bat [fridge ect] ,,, also have 3rd bat in trailer.. 6mm wire from 2nd bat to 3rd thru 7 pin plug + and - ,,,pin no2 aux or reversing sig =neg,,,,pin no5 elec brakes = + power,,,,system works as no need for brakes on our trailer [under 750kg] power LOSS is minimal,,,, bat charge rate at idle,main 14.8,, no2 14.7 no3 14.6volts,,, the beauty of the system is that only 1 plug to connect,,and is easy and cheap to cofigure,,have 6 power points in trailer for lights and fridge ,radio ect// when trailer independant of car ,power lasts 4 days/nights,,plugged into car ,3rd/2nd bats in series , power for7/8 days without starting vehicle ,,, always recharge bats when volts drop to 10.5 never lower,,,,takes35/45min at idle to bring back to FULL charge ......