vhbw Battery 2500mAh brush Braun Oral-B Professional Care 8000, 8300, 8500, 9500, Triumph 4000, 5000, 9000, 9400, 9500, 9900 as 3731 (Electronics)
Purchased in December 2013; takes just 2 days, 15 months later. Product inexpensive initially, but its short life the fact very expensive in the end, not to mention the tedious process of replacement (battery soldered) on OralB brushes.