There is a far easier, and cheaper way to accomplish what you want. Simply install a battery cut-off switch, and wire the electrical feed to the radio before the switch. That way, the only drain on the battery will be the radio. -Robert vin 6585 "X" --- In dmcnews@xxxx, "Hank Eskin" <henry@xxxx> wrote: <SNIP> Is there a way to wire a second battery to the radio that will power > the radio, but not also feed whatever is draining the charge of the main > battery? If someone can describe the schematic and required parts, I can > build it. As a bonus feature, I'd like this circuit to allow the aux > battery to be charged like the main battery when the car is running. <SNIP>