Originally Posted by Ob1
Mount your inverter as close to the battery bank as possible . . . AC line loss is minimal compared to DC line loss . . . .
To be more precise, higher voltage (120 volts) requires less current per watt and produces less line loss than a lower voltage (12 volts), which requires a higher current per watt. Current
flow through a resistance (the wiring) produces heat, which is wasted power.
Raising the voltage decreases current demand and therefore reduces wire heating loss. This is why coaches will often have 24-volt systems. Some inverter systems (including a tiny number on bus conversions) will use a 24-volt or even 48-volt battery bank and a matching inverter with AC-only wiring. These inverters are not department-store finds, though.
If one were to go this more expensive route and still want to add 12-volt DC devices, use a DC-to-DC converter for them. Tapping across the first battery (or first two 6-volt ones) will screw up battery longevity. The cheap and smart way, as stated by others, is to put a 12-volt inverter near the batteries, use heavy wires, keep them short, and keep connections tight and clean.