Quick Question RE: Tear, Archangels

How does the "Mana Charge" passive work through the upgrade? In other words, if I build up +600 max mana on a tear & then upgrade it to AA - does the +600 max mana from tear stay in my pool and AA starts another "Mana Charge" passive at 0? Or does the AA keep that +600 going, until it reaches +750 and transforms into Seraph's Embrace?

Hope that makes sense, and thank you in advance for answering a newbie question