@Meddler: Can I get your opinion on a "heavy health cost" ultimate for a juggernaut?

The above link is to a juggernaut Champion I'm working on that can tap into a powerful but cursed sword to give her a massive power boost, but costs her a large amount of health per second (with a steadily increasing upkeep cost). However, getting the health cost to a suitable amount is tricky. I know concept makers aren't really supposed to try and balance numbers on their own (as we never get it right), but even getting close would make things seem more legit.

Here's the ultimate for context. You can check the above link for more if you need to.

#R - Ebonmere Toggled Off: Celes gains 10/15/20% bonus lifesteal. Celes does not receive this bonus while Ebonmere is toggled on.

Toggled On: Celes taps into the power of the Ebonmere, granting bonus effects on her basic abilities and +30/45/60 bonus attack damage; this attack damage bonus increases by 1.25% for every 1% of Celes' missing health, maxing out when Celes is below 20% of her maximum health. However, Celes' base life regeneration is reduced to 0 and she loses health equal to 2% of her maximum health every second. This upkeep cost increases by 6/8/10 health every second. Ebonmere automatically deactivates if Celes drops below 5% of her maximum health.

8 second cooldown after deactivation. Cannot be deactivated during the first 3 seconds after being toggled on. Celes cannot activate Ebonmere if she is below 10% of her maximum health.

Being a juggernaut, Celes is supposed to build stuff like and , so I question whether the values I've selected for the upkeep cost increase are too low.

If you have a moment, can you lend an educated opinion?