Multiple battery system
A multiple battery system (often a dual battery system) is an addition to a vehicle's standard fitment of one single combined starter and utility battery. There are several vendors of these types of systems, and some people go for a DIY approach. Some vehicles come with dual starter batteries in some markets.
Benefits of installing additional batteries include larger combined capacity and the option of isolating the starter battery so that "house" loads don't drain it during periods of rest.