BMW Questions? Ask a BMW Repair Expert for Answers.
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it is posisble that a faulty water pump or thermostat could cause battery discharge, but it is not terribly common.
if you do not have a coolant leak or low coolant level, it would be advisable to replace both the thermostat and water pump (they are normally replaced together as a best practice that is pretty strictly followed).
to verify the cause of the overheat and/or the battery message, you would need to have the fault logs read from the car using a BMW scan tool. The water pump is very common to fail on this model and if you have not had it replaced you are overdue to replacing it, along with the thermostat is going to be a good idea regardless.
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