Fleet Carrier Weekly Upkeep in Elite Dangerous.
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Fleet carrier weekly upkeep is deducted from the carriers account on thursday's weekly Elite Dangerous server maintenance (also known as galaxy servers).
If your fleet carrier account doesn't have enough credit balance, then you are given an emergency loan. Now this doesn't mean you can just ignore all those weekly maintenance fees, you will pay back the loan and if you do not your fleet carrier will be decommissioned.
As said if you fail to pay your weekly maintenance fees, then your fleet carrier will be decommissioned. I don't know for a fact what happens to any ships and modules you have docked/stored in the carrier, logic say that they will be transferred to the nearest starport/station, however I never decommissioned my carrier so I don't have first hand experience.
Fleet carriers weekly upkeep is activated/charged/counted the moment you turn on a service, so don't turn services on just briefly, only turn them on and keep them on the whole week if you really need to. It is my understanding that if you turn on a service even for a 15min period, you still get charged the full weekly upkeep from that service which can be hundreds of thousands or millions (cant remember how much each is).