I bought 3600 mAh and I like it although not the cover (plastic). I used it together with the SD mod from craves1 and this worked well. When you bought N810 were you content with the battery life? If yes, then 1800 mAh (verus 1500 mAh of stock battery) will be OK, and you can use your current battery as reserve. If you weren't happy with battery life then 3600 mAh would do it.