Chosen Solution
After battery replacement side bottom of my iphone 6s is not working. When I put lightning cable with power supply in it the decives starts. But I can not look by clicking on on/off (side bottom). In meantime I got the possibility to reset my iPhone with iTune on another PC but without success. It seams to be that I damaged cable on upper left hend side during battery change. Therefor I ordered a new cable and let you know.
Depending on how you removed the old battery you may have damaged the power ribbon.
