[Rob_of_Waterloo]

Hello folks

I am nearing the completion on my Miata conversion and have a question about the dc-dc converter. I have a 750 W (62A) dc-dc converter and plan to leave the original car (aux) battery installed. Input power to the dc-dc converter is disconnected when the ing is off. The dc-dc converter is connected directly to the battery.

I am concerned that the output stage of the dc-dc converter will slightly drain the aux battery when the car is off. Even though this will take a long time, I am interested in what other people have done. I can think of few different options

1) Always power the dc-dc converter, even when the car is off. (not preferred)
2) Have a power diode between the dc-dc and the aux battery
3) have a power relay between the dc-dc and the aux.
4) directly connect the dc-dc to the aux battery.

I am leaning towards option 4.

Thanks for any input.