Connecting auxiliary battery charger IC to mobile chipset

A method and apparatus for connecting an auxiliary charger IC (52) to a mobile platform chipset (52) so that charger connection (64) wakes-up the power management unit (50), operating system or charging software as soon as there is enough battery power for operating system to run the charging software. The apparatus comprises: a power management unit (50) powered by the battery (24); and an auxiliary charge controller (52) powered by the battery (22) or by power from any one or more of the charging power sources (64); the method comprising the steps of: the auxiliary charge controller (52) generating a first wake signal (56, 58) upon detection of a charging voltage at any one or more of the charging power sources; the power management unit (50) booting or waking the operating system upon detection of the wake signal; and determining whether the operating system has woken or booted correctly; characterised by: upon determining a boot or wake failure of the operating system, the auxiliary charge controller (52) generating a second, periodic wake signal (50, 58, 56) until it is determined that the operating system has booted or woken correctly.