# Estimating current draw from alternator (14.4v?) to 12v DC

I'm wiring my caravan into my car this weekend. In order to keep the caravan's leisure battery charged the cars alternator provides a current to the caravan for this purpose.

I need to figure out what gauge wire and fuse I need for this.

Unfortunately my multimeter can only measure up to 10amps DC and I don't want to kill it in the process of measuring the current from the car. I intend to let the leisure battery drop to 12v (about 50% full) at most. I think the voltage from the car is about 14.4v for charging the leisure battery, or around that.

I'm not sure how to calculate a current draw between two voltages.. I suppose a lot of it has to do with the fact these are lead acid batteries?

Some guidance would be very much appreciated. I couldn't find the answer on google.

• Will the leisure battery be 80% drain before you start the next trip again? – Jason Han Aug 5 '17 at 13:32

And as for finding info, this link may help :http://www.12voltplanet.co.uk/split-charging.html