The only way to charge the power of Leonidas's spear would be to collect the Artifact Fragments from each member of the Cult of Kosmos.
Upgrade the Spear
Related points of interest
Objectives of Upgrade the Spear
1. Collect Artifact Fragments 1/3
2. Upgrade the Spear
Return to the Ancient Forge at Andros (you can fast travel there) and upgrade your spear.
