Describing it as the Holy Grail of mobile computing, HP says it has developed an ultra-capacity battery that can run for 24 hours on a single charge and has put it, as an option, in a new XP-only EliteBook 6930p notebook.

However, HP warns that battery life will still vary depending the product model, configuration, loaded applications, features, and power management settings and says the “maximum capacity of the battery will decrease with time and usage.”

Evidently the battery owes much to energy-efficient notebook components like Intel’s new low-power solid-state hard drives (SSD) and an optional mercury-free 14.1-inch LED display that reportedly boosts battery run time by up to four hours compared to traditional LCD displays.

HP said the SSD provides up to a 7% increase in battery life compared to traditional hard drives.

The notebook, which weighs in at 4.7 lbs to start, will be available in October. There’s no pricing yet.