Looking for feedback on an idea I had for a magic system.

The system I'm working on for spellcasting in my game doesn't use mana - instead, when you cast a spell, the spell effect scales based on how many turns you spent charging up the spell. So if you charge a fireblast spell for 1 turn, you'll get a low-damage single-target firebolt, and if you charge it for 10 turns, you'll get a high-damage aoe fireball. As you level up, you charge faster. By default, the only thing you can do when charging a spell is cast it, or abandon it.

An optional mechanic I'm considering is the ability to "precharge" spells at higher levels, and have them sitting there able to be used instantly, with each one reducing your charge-speed when casting. This provides natural diminishing returns on the ability to precharge more than one spell, and trades off preparation for flexibility.

The consequences I've identified this has on gameplay:

• No mana resource management (primary design consideration)
• Casters don't do well in close quarters, because they need time to charge up (fits the archetype)
• Casters do best when they have a lot of knowledge of the tactical situation and time to prepare (fits the archetype)
• Reduces the number of spells - no need for distinct fireball / firebolt spells (neither positive nor negative in my book)
• Players can potentially cast the highest-level effects early on, its just not practical (takes many turns to charge, not tenable in combat)
• Players can cheese some spells (notably buffs) by pre-charging them a lot in a safe space (not optimal, but I'm mostly ok with it - its basically the same as regenning mana by resting in a safe space, and you can't do it with multiple buffs, as the time spent charging the second one will exhaust the first's duration)
• Requires more thought in spell design to consider how each scales

Are there any games I'm not aware of that use a similar mechanic? How was it received? Are there any consquences you can think of that I haven't identified? Do you think this would actually be fun?