A priest of Ra might recharge when he is praying in a temple of Ra when the sun is shining. This is a CONDITIONAL MANA RECHARGE.
A druid may recharge by performing a ritual at full moon, which is a SLOW MANA RECHARGE.
A fire warlock might choose to recharge by playing with a fire, something that can easily be done under most circumstances. This is normal recharge, unless he takes FAST MANA RECHARGE, in which case he will recharge at twice normal rate, 1/7 of the SAFE MANA LIMIT.
A female shaman of a barbarian tribe may have her mana recharge coupled to her menstrual cycle, having the mana tally reduced to zero once a month. This is a SLOW MANA RECHARGE combined with COMPLETE MANA RECHARGE and AUTOMATIC MANA RECHARGE RITUAL.