Reference

Notes on an Extended Battery Pack

This topic explains battery charging behavior when an extended battery pack (not supplied) is attached to your VAIO computer in addition to the installed battery pack (the primary battery pack).

When the battery care function is disabled, the battery packs charge in the following sequence.

The primary battery pack charges to about 80% of its battery capacity, then the extended battery pack starts charging.

The extended battery pack charges to about 80% of its battery capacity, then the primary battery pack starts charging to 100%.

The extended battery pack starts charging to 100%.

The battery power of the primary battery pack will be used after the extended battery pack runs out of power.