We've been working hard on bringing this one to the U.S. It's the most simple, cleanest and most affordable dual-battery system on the market. Just run a cable set to your engine's start battery, and your ready to go. With it's built-in voltage sensing relay, there's no need for complicated charge systems or external isolators.
From Hard Korr - Manufacturer:
HEAVY DUTY BATTERY BOX WITH VOLTAGE-SENSITIVE RELAY (VSR)
Our heavy duty battery box allows you to turn a regular deep-cycle battery into a convenient portable power station or create a dual-battery setup using the inbuilt VSR. It is suitable for all deep-cycle batteries up to 330mm x 175mm x 220mm and up to 130Ah.
Constructed of durable ABS plastic and meeting the UL 94V-0 standard for flammability of plastic products, this battery box is a high-quality unit that will last for many years. It contains two 12v outlets with 10A fuses, a dual USB outlet, four 50A Anderson-style outlets that can be used as outputs or inputs (one reserved for VSR input), and a 175A Anderson-style outlet which can be used as a jump-starter. Unlike most other models on the market, all Anderson-style ports are recessed into the body to minimise the possibility of damage, and the internal cabling uses heavy-gauge wire and quality connectors.
The battery can be charged from a range of sources (including solar panels) by simply plugging into one of the 50A Anderson-style ports, or directly from the vehicle’s crank battery using the VSR. The battery’s charge status and voltage can be easily seen via the large digital display.