fridge battery

Emmet

More info might be helpful............

Where do you plan to locate the gel battery?
What type of auxillary socket are you talking about?
Do you plan to incorporate a isolating solenoid?
What type of vehicle?

My suggestion is to use heavy cable (min 8mm) from isolator to the gel battery. If, by "auxillery socket", you mean the cigi lighter socket, I think you will find they have a very small amount of current carrying capacity and should only be used for powering small accessories; not for charging a 2nd battery of any type.

Do the job right in the 1st instance and you won't have to be mucking about with it for a long time.

Not an ideal situation to charge like that. The wire size to a standard auxillery socket is generally too small to take the full charge when the battery is flat & may just result in blowing the fuse. Cheers Craig...........

No, not at all advisable.
Auxiliary sockets are usually fused to a maximum of 10 amps and have suitable wiring for around a 5 amp load.
Get a proper sized cable and plug system fitted - preferably Anderson style plugs $20.00 a pair.

Emmet

Despite what many people say, I have been doing it for years, with no problems.
However there are a few things to consider. Firstly gell cell batterys need to be stored in a cool place eg. anywhere BUT under the bonnet. Also you must keep the charge rate around 13.3 volts and the current should be well under 10 amps.
I built a 13.3 volt regulator with parts from Jaycar for around $15 that does the job and it plugs into a cigarett lighter socket, that so far hasn't blown a five amp fuse.
The batterys are in the back of the wagon and power my waeco FF70 for two days in moderate weather and it takes around six hours of driving to bring the batterys up again.

Chaz