1948j

Have bought my daughter. 10 plate grand voyager. Have problem rear door driver side stopped activating electronically. All results of searches show doors with a form of rack and pinion track moving the door back and forth. This one has no rack and pinion system it has a cable arrangement. Was working but has suddenly stopped. Will work manually if engine has been running but after sitting a while it refuses to do anything. This I assume is a battery problem. But what is the cause of the electrics not working the door. Any ideas please.