Is this homebrew feat allowing casters to convert hp to spell slots balanced?

Question

Is this feat balanced?

---

Prerequisite: The ability to cast at least one spell.

You can sacrifice hit points to regain spell slots.

When you cast a spell slot created by this, roll 1d20. On a 13 or lower, the spell does nothing.

You may expend:

• 10 hp for a level 1 slot.
• 25 hp for a level 2 slot.
• 45 hp for a level 3 slot.
• 70 hp for a level 4 slot.
• 100 hp for a level 5 slot.

You can spend additional hp when regaining a slot to add a modifier to your roll to see if the spell is cast.

• You gain +1 to the roll for every 2 additional hit points you spend to cast a level 1 or 2 spell.
• You gain a +1 to the roll for every 4 additional hit points you spend to cast a level 3 or 4 spell.
• You gain a +1 to the roll for every 6 additional hit points you spend to cast a level 5 spell.

Answer 1

This can be Exploited at your table to gain Infinite Spell Slots

It would only require the DM to permit multiclassing, at which point a player need only do the following:

• Take one level of Cleric, in the Life Domain
• Take one level of Druid,
• Prepare the Druid spell Goodberry
• Cast the spell, generating 10 berries that each restore 4hp (confirmed by RAI), restoring 40hp in total
• Spend 10 hitpoints to regenerate the 1st level spell slot
• Spend 24 hitpoints when casting the spell to guarantee spell slot recovery, generating 10 more berries
• Have 6 hitpoints left over (1.5 berries)
• Use excess healing to recover other Spell Slots

So any character with this feat and those two class levels (requiring only a wisdom score of 13 or higher) could recover all their hitpoints + valid spell slots so long as they have a single 1st level spell slot open.

Another example:

• One level of Life Domain Cleric
• Three levels of Druid (any Circle)
• Prepare Healing Spirit
• Cast Healing Spirit on yourself
• Spend 25 Hitpoints to recover the spell slot
• Remain in the Healing Spirit for 10 rounds, recovering 10d6 + 40 hitpoints (75 average, 50 minimum, 100 maximum)
• Spend 24 Hitpoints casting Healing Spirit again
• 1 hitpoint remaining at minimum, 51 hitpoints remaining at maximum, 26 remaining average
• Use excess healing to recover other Spell Slots

---

These are only the most obvious exploits I can think of. I'm confident there would be other ways to abuse this mechanic.

Answer 2

Very unbalanced

This does not factor in different hit die for different classes.

A Wizard (and Sorc) only have d6 hit die which means if they are REALLY good, they can regain a 1st-level spell by the time they hit 2nd-character-level but more likely 3rd.

However a Ranger has a d10, which means that by the time they can cast their first 1st-spell-level at 2nd-level, they have room to spare.

Most other spell caster classes have a d8 hit die which means they probably can't use it until at least 2nd, but maybe with a good CON can pull it off.

They higher up in character class the more divergent the ability is. Wizards and Sorcs will be struggling with hp while other classes will be much better off.

Answer 3

This could work with a vampire thematically. Make it so healing magic doesn't work on them, and they can only gain gain heal by drinking blood. They they can spend their hp to cast spells and drink blood to restor slots. The other thing. Is that the health costs are a bit high. Most wizards will only have 140 hp at level 20. Using most of that to cast a 5th level spell is a little dumb. Just making it 10 per spell level is better. Not as game breaking as the rest of the stuff wizards can do at higher levels.