I asked this same question to the forum a couple of months ago (haven't searched for the thread) and I think CT answered it. In summary, 110 may prolong the battery life, but only very fractionally, based on the specs of the battery. My impression was it really is fine to use 220 without any long-term battery life concerns.
*UPDATE* The discussion about Level 1, 2, & 3 charging, and effects on battery life are here
. And it was Kab who answered the question. Hope this helps.