Battery dicharge/fan issue - any ideas?

[FlipFlopGriff]

I've had this problem for a while now. When I turn off the ignition the batery light stays on at the bottom of the speedo and gradually fades away over about 60 seconds. It only happens when the fans are on and I switch off though. I also have the red light at the top of the traffic lights dimly lit all the time but you can only see it (and its quite faint) when driving in the dark. The battery tends to drain relatively quickly but I keep it on an accumate now so no real issue. The voltage only tends to read slightly above 13 also and with the lights on a shade less than 13 but I've had the alternator checked and its fine.
Any ideas?
FFG

[spend]

Your alternator needs a new brush pack clipping on the back (reg & diodes are in the pack), easy enough job.