Main salon battery switch access under steps

[Viper]

Unless the generator battery is somehow connected to the other banks, that shouldn't be the problem. Generator batteries are usually isolated from everything else, in other words you can't select it as a bank to run your engines or house systems, so that wouldn't be the one you're noticing to be losing it's charge and it's separate charger shouldn't be the issue.

[km1125]

Touch each alternator when the engines are cooled down and see if one is warmer than the other. It's not very common, but you can have a failed diode (recifier) inside the alternator that will cause a drain whenever the engine is connected to the battery.

[Phrancus]

5.8 amps of draw.

that's a lot. Not a simple light or standby device. Lot's of good suggestions above. I might add: perhaps there is a device connected in a wrong way. Either on purpose like a bilge pump that has a connection through the breaker panel and one around it for continuous standby. Or by mistake when a connection was made in a way that current flows when a plus becomes a relative minus. Or through a damaged wire that does not cause trouble when all is powered with enough amperage to allow for the leaking but does when the supply is gone.

My advice: disconnect all, reconnect one by one. Start with the generator as suggested above, if that provides the source. go on and check the rest one by one anyway as this will help you in the future.

[tomschauer]

I personally would start with that Zantrex charger / inverter. They had a really high failure rate.
I would disconnect it totally and see if your drain doesn't disappear.