You can store one power that you can manifest in a weapon of your choice. Only one such power can be stored in a weapon at a time; you cannot have more than one empowered weapon at any given time. You can store a power costing up to your manifester level minus 4.
You expend the power points for the stored power, including augmentations, when you empower the weapon initially (in addition to those spent to manifest empower weapon). Once the power is stored, you can manifest the power from the weapon without expending power points from your own reserve. You can manifest the power stored within the weapon as you stored it, complete with its chosen augmentations.
For example, the 14th-level psychic warrior Ragnara knows both empower weapon and oak body. She manifests empower weapon and chooses to store oak body augmented with 1 power point (the maximum allowed at her manifester level minus 4). At the time she manifests empower weapon and stores oak body, she spends 19 power points (9 for empower weapon and 10 for the augmented oak body). Several days later, when she manifests the stored power, she does so without any power point expenditure.