Battery relocation :
1. Use quality cable
This involves avoiding halfords , yeah I know they open on Sunday's ,but they stock total shit , they source Chinese shit , wherever possible as it maximises profits . -Avoid
Cheap Chinese cable use a plastic outer insulation , this has poor fire resistance , read about as close to zero as is possible , it also has poor conductor wires - so the cable has to be thicker as a result .
The longer cable run at high current can drop voltage along its length .
Quality cable will be at least 2 cable sizes thinner , carry the same current , has insulation good to 400volt plus (despite being thinner) and will withstand a direct short circuit or fire for 10 mins - this gives you time to pull over and switch off ignition .
A circuit breaker is a good idea , next to the battery , and quite cheap around £25 , breakers need to be in open air if possible ( not buried under carpet or such ) as they are thermal devices .
Fuses and breakers actually pass more than the rating on them but only for fractions of a second and if too warm will keep tripping as a nuisance - breakers are better than fuses .
Try a test : get 3 inches of halfords cable and put under a fag lighter - watch what happens = your car full of black choking smoke and on fire !!! - causing more short circuits as it burns !!