Cost efficient, yes, but energy efficient, I'm not so sure.
Don't understand? The 240V transformer generates heat as does the battery charger. Both are negligible. Am I missing something?
The power supply mode has enough capacity for all my needs. The whole idea of using power supply mode is so that my batteries do not cycle. Or that is my understanding anyway. Perhaps somebody could correct me and I may have to rethink my power use.
KB
I assume energy efficient as you are not using the battery charger which has its losses. I doubt a battery charger is efficient, so if not needed, don't use it?
Less heat as there is less equipment running if the battery charger is not used to provide the 12V for the fridges. Would you need the battery charger on to trickle charge battery? Once it is charged, turn off the charger.
The charger will get hot to keep up with the 12V drain for the fridge(s) changing 240V to 12V. Needless losses producing heat.
Does the fridge(s) have the same wattage rating on 240V as on 12V?
In "power supply mode", does the charger just see the fridge use (when compressor is running) and think the battery needs a bit more of a kick along. Just current or more volts?
There is no guarantee all the fridge and other power requirements will come from the charger alone. Some chargers in "power supply mode" provide a lower voltage than when in normal charge mode. Ie, the battery can have a higher voltage than the charger supplies in "power supply mode".