Have from this dealer Months 6 a spare battery bought for a Gigaset 4000 Micro works flawlessly until today (before that I had at the Micro also has a spare battery of Ebay in the use of worked flawlessly). Therefore, I have a SL1 color buy here again and also this battery works perfectly so far. Of course I can in the short time within 1 week hardly write something on the reliability but I will charge tests the phone for about 4 days in standby mode without it (almost no phone calls) and the battery still displayed on the phone with 100% capacity , As I recall, the original battery was not much better. Times the replacement battery last as long as the original Lives hope were so nearly 9 years (from date of purchase SL1 10.2005).