A diode will prevent 'backflow' of current. But that might make charging it, when you want to, more difficult. The easiest thing would be to disconnect the battery when not needed - using the plug (of it has one) or hook up a disconnect switch.

Hello

Most have only one socket and this is for the lights. If you have a battery on it that charges from the car you will normally have a second socket dedicated to do this. Consult an Auto Electrician as this sometimes can also include a switching system which decides if to charge the car battery or the one in the trailer.

Andy C

If it's a 12 volt system I don't see what the problem is.

If it is all wired up properly, there will be no problem.

I have a battery pack and that is getting plugged into a trailer to power the lights and sometimes they have a battery on them. How can I prevent the electricity from going from the trailer battery(if one present) and frying my battery pack? A diode? A fuse? Best way to do that.