Final iteration of the power supply?

I hope so, but I will find out soon enough. More about the Aviogard and DC-DC converters in general can be found here. These are the premises for the power supply to the secondary system. The primary system is standard, as set by the engine documents.

• Only sensitive instruments, delicate electronics with little or no protection on their own
• I need a backup battery, or I will lose every bit of info in case of a main battery failure
• The backup battery must not be too large.
• The backup battery needs to be charged by a real charger. A DC-DC converter is not a charger according to Mascot.
• A DC-DC converter with a galvanic barrier will isolate the secondary system from the primary.
• The DC-DC converter must be able to have a battery as the load without entering into hiccup mode for some reason or the other.
• The charger draws 2 amps max. It us put on the primary side to off load the DC-DC converter.
• The charger allows visual inspection of the state of the backup battery
• Make it as simple as possible (feels like this is a joke at the moment, but it's actually not much more complicated than the first iteration with the Aviogard, which doesn't work).
• If it dosen't work, remove the DC-DC converter and replace it with a secondary master switch.

The system looks like this: