Apparently it isn’t that hard to survive the 248 damage from upgrading it. 155hp, 92 shielding from self-targeting with wand and Scroll of Challenge halving the damage. (ShPD 2.2.1)
I usually just pop a potion of shielding.
How much shielding does that give?
Don’t know the exact numbers, but I’d say about 120 on high levels.
Edit: Just tried it. At max level you get 115.
Pricking yourself to level it up from +9 to +10 does 248 damage. You’d need to be level 28 and at full HP to not die with just a Potion of Shielding. I’ve usually beaten the game before I hit 28. Much easier to use a Scroll of Challenge or a Blessed Ankh and actually get some use out of the +10 Chalice.
Yeah, I usually save my experience potions to get to level 30. And of course some of it is absorbed by the armor. Just took 229 damage to get to +10.
There is also blandfruit+starseed
The wiki gives a table to help. There’s a minimum level where you can upgrade the chalice with or without a potion of shielding.
