Victron - Cyrix-ct 12/24V-120A Battery Combiner Kit Retail [CYR010120110R] MultiPlus 12V 230V and unlike many other products

and unlike many other products that state universal input

but isolates the starting battery when charging ceases so you never get stranded

and 48V systems

The alternate source typically is an inverter

Victron - Cyrix-ct 12/24V-120A Battery Combiner Kit Retail [CYR010120110R] MultiPlus 12V 230V and unlike many other productsThis Battery Combiner Kit is for adding a 2nd or 3rd battery system in your car, boat, RV or any other vehicle. It utilizes the simplest and most advanced technology to keep all your batteries charged using the engines electrical system, but isolates the starting battery when charging ceases so you never get stranded.