Engine load when circuit de-isolated

[Fergus3060]

Spurred by a recent post about a Battery Isolator switch and bilge pump I have had a thought about how I should power the boat at anchor when overnighting somewhere.

I have just wired up the boat in a similar way to this system:

https://www.bluesea.com/systems/42/2...ctrical_System

The only '24hr' circuit I have connected directly to the battery is the bilge. The rest are on a fuse panel/bus bar that's isolated with the main switch. Ideal for leaving the boat on it's mooring.

However, I've only just thought about anchoring. For the all-round white light to function, the main isolator switch needs to be made. That means all the other circuits will be live, including the engine harness, nmea2k etc. VHF/chartplotter etc have their independant switchgear although fused by the fuse panel/bus bar.

So my question is, with the engine off and ignition key out, is there likely to be much of a draw from the engine/nmea to need to worry? I realise there's the second battery that is there to connect if needs be, but its not ideal to build in a draw that can't be isolated. (engine is 2018 Suzi 250 with smg4 gauge)

[jeffstevens763@g]

Do a separate switched and fused feed for the light straight from the battery would be my answer

[Limecc]

Easiest thing is to put a multimeter in series in the circuit and measure the draw in mA, then we can calculate how long your battery will last to 50% charge.