hi Hakim_Radzuan, my E60 also just flashed the "High Rate of Battery Discharge" signal on Monday for few times. It came up few times when I started the car at the onset. The clock was reset to zero hours. Have to reset. Sent to Auto Bavaria but that guy at Glenmarie has no clue to what I was trying to tell. Instead he made an appointment for me to send the car for a complete checkup, appt only 2 weeks later on 5 May!
But the next day, there was no more signal on Battery Discharge.
I'd be interested to know if your mechanic has diagnosed and solved the problem.