When Dell Power Manager is turned on, battery consumption on linux is almost on maximum - that means around 23W. When power manager is turned off, power consumption can be reduced (gpu turned off, wake on lan turned off, display brightness decreased, cpu clock speed reduced etc) to 10W. There is no linux power manager (but this applies to almost any notebook except few thinkpads).
Battery died out after aprox. 2.5 year - after battery was disassembled it looked like in one serial pair of two batteries died. Problem was that it does not meant rapid capacity drop, but instead rendered battery completely unusable. It looks like it is normal lifespan of that battery type (many people report sudden death of their battery pack on 5537).