Ok so for those that don't know, If you side with the Volkihar you gain Access to the Bloodstone Chalice, an item that when interacted with makes your Drain Life spell also drain magicka and stamina for 1 day.

By doing various radiant quests in which you collect ancient vampire body parts you can increase the longevity of the effect by 2 days per quest.

My question is this, is there a limit to how much you can extend the effect as I currently have it on 9 days and is it possible to upgrade the effect in any way that isn't increasing the longevity?

im at 8 days right now.
truthfully though if it did anything it should have increase the damage for vampiric drain,not let you absorb magicka and stamina.

True, though the absorb magicka bit is useful as it allows you to pretty much chain cast the attack, though i am still looking for any possibly way to increase the damage of the drain life ball attack, anyone have any idea how to do so?

drain life ball? the VL attack? if so i dont think so,but if you have serrana following you around it will be weaker.

Indeed, a terrible bug as many people don't even realise its a bug and just consider the Vampire Lord Form to just be weak as hell