Since inverters can exhibit very high amperage draw from the batteries, you should always use dedicated cables of the proper size, taking into account both the cable length and the sizing specified in the installation manual. In addition, a properly rated fuse system ( class T preferred) should be located in the positive cable within 18"-36", depending on which standard you wish to apply.
I would never depend on any existing cable structure when installing an inverter.
RVIA/RVDA Nationally Certified Master Tech
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Master Tech Energy Systems, Inc.
AM Solar Certified Installation Center*AMS Lithium Batteries
Lifeline AGM Batteries**Magnum Inverters***Victron Energy Components
Lew Farber...RVIA Certified Master Tech...ABYC Certified Master Marine Electrician
SOLAR TECH ENERGY SYSTEMS, INC.
AM SOLAR ...MAGNUM…VICTRON ENERGY...LITHIUM & LIFELINE BATTERIES…MARINE REFRIGERATION