Per the DMG, pg. 118, Magical Research and the Fabrication of Magic Items.
The renewal of arcane charged magic items (rods and staves, some wands, etc.) may require the casting of Enchant an Item, as well as any spells relevant to the function of the item. Casting Enchant an Item requires 3-10 days (2 + 1d8 days), and remains in effect for as long as the item has not been used. Charging does not need to take place on consecutive days.
Each spell imbuing adds charges equivalent to the number of charges the effect would use (Burning Hands = 1 charge, Fireball = 3 charges). Applying charges does not interfere with potion brewing or scroll preparation.
Unlike permanent, non-charged items (such as a magic ring), Permanency is not required for creation or recharging.
What can be recharged by clerics: Rod of Beguiling, Staves - Command, Curing, Striking, Withering (the latter does not specify one way or the other so I am inclined to say it CAN be recharged; however, for good clerics this item might be considered problematic and some deities will absolutely not approve recharging them)
The process is sort of similar to that for magic-users in that it leverages the magic item creation rules. A cleric of name level (9th or higher) must prepare the rod/staff for recharging. This is accomplished by spending one week in complete isolation for meditation and prayer with the item. Then, one full day must be spent praying over the item and invoking the blessing of their deity (thus, 8 days total). At that point, spells may be cast into the item to recharge it as per the magic-user method. If the item is used, it can no longer receive further charges until the process is repeated. Only one item can be "eligible" for recharging at a time by each cleric. Only that cleric can actually do the recharging.
Notes: