niteliter,

I may be reading this wrong but it looks like you want to pull out the 1800mah and replace it with the 910mah? If that is what you said then you are going the wrong way for more flying time.

If you are going from the 910 to the 1800 then I think it might be too nose heavy being that the 1800 is longer and won't fit nicely into the holder. The added weight might be the true problem here. The more weight it has to support to keep off the ground the less flying time you will have. I use the thunder power 1320mah 11.1 in my cpv3. It is the same size as the stock battery but it is lighter.

If you are getting 10-12 min consider yourself lucky! Are you pushing your batteries too far so they might get damaged? I get about 7-8 before it tells me it wants to land. My suggestion would be to just get more batteries rather than push the edge.

Another thing I would be concerened with is the tail motor. That thing gets super hot and a longer flight would add more time to the excessive heat and you might burn out your tail motor faster.

Just my two cents, Happy Flying