To recharge enchanted weapons in The Elder Scrolls IV: Oblivion, you have several methods:

• Use Soul Gems: The most common way is to use filled Soul Gems. You can fill empty Soul Gems by casting the Soul Trap spell on an enemy and then killing it, capturing its soul. Filled Soul Gems can then be used to recharge your weapon's charges. Larger Soul Gems hold bigger souls and recharge more charges. Black Soul Gems are the best but harder to obtain. This method is cost-effective but requires some effort to gather souls

• Use Azura's Star: This is a reusable Soul Gem obtained by completing Azura's Daedric quest. It functions like a Soul Gem but never breaks, allowing you to recharge weapons indefinitely without needing to find new Soul Gems

• Use Varla Stones: These special items fully recharge all enchanted weapons in your inventory at once. They are rare and found in Ayleid Ruins, so it's best to save them for late game when you have multiple enchanted weapons

• Pay a Merchant to Recharge: Various NPCs in Mages Guild Halls and the Arcane University offer recharging services for a fee (about 1 gold per charge). This is the easiest but most expensive method and not recommended if you want to save gold

To summarize, the most efficient way for regular play is to use Soul Gems filled via Soul Trap spells, possibly aided by Azura's Star for reusable charging. Varla Stones are useful but rare, and paying merchants is a last resort due to high cost. You can check your weapon's charge status in your inventory by enabling detailed view and selecting the weapon to see current charges and uses remaining