Following the above advice, I bought one of the batteries mentioned in the above post, for my n810.
It came last week. It's obviously heavier than the cheap batteries that last 40 minutes, and a tighter fit too.....I had to carefully sand some off the end of the battery to make it fit well.
After charging, it gives the full 1500Mah that the original battery gives, Battery Monitor reports about 6 or 7 hours of life, and using the n810 reduces reported battery life about the same as the stock battery.
Thanks for the tip!! I was about to bite the bullet and buy a Mugen battery, at about 4x the cost, but I don't need to do that now.