You can put an inline fuse holder in the wire itself, then you can use whatever the unit is rated at. I put a permanent live feed to a aux socket to keep an led inspection lamp charged all the time, I connected this direct to the battery then put an inline fuse holder and fuse in. This means I can run any 12v item from the boot without the ignition being on and I can swap the fuses to meet the spec of the item being used.