Garen + Warmog + Spirit Visage = Regens approx. 15% of max health per 5 seconds out of combat
Garen's passive: 10% of max health per 5 seconds while out of combat level 16+.
Warmog's: 3% of max health per 5 seconds while out of combat.
Spirit Visage: Multiplies the above by 20% and adds 100% base health regen.
Total: Approximately 15.6% of maximum health every 5 seconds when Garen is out of combat, not including regeneration he gets from his base regen and other sources.
#Bottom Line: TOO POWERFUL.