Well in my case, it seems to have been due to cpu-consuming faulty applications running all the time. Today I did not have any problem anymore (uninstalled the suspicous widget). Got to say that without that problem my device gets a remaining about 90 % of charge after a work-day (all wireless lan and wireless mobile data off), just beeing in standby. But in the evening and with heavy using wlan, it goes down rather quickly ;-) I will now try to reinstall the widget anew and reflash if the same error will occur until tomorrow.