I my case both the N900 and the N9 barely lasted for 12 hours when used in an active way. Less under heavy use.

I then tried a Galaxy S4 and it cured that problem by lasting a minimum of 12 hours easily even under heavy use. However one has to note that the S4 is not exactly a power-saving device. Quite to the contrary.

I now use a S5 since a couple of weeks and any endurace problems have simply disappeared. The somewhat larger battery but also the hugely (>=30%) reduced power draw compared to the S4 makes this thing last forever. The S5 is the first smartphone where I simply have stopped worrying or even thinkg about remaining battery levels. Forgot to charge, only 30% charge left at the start of the day -> no problem. Ultra power save mode claims standby times >10 days. I have not yet put it to the test but I believe it's a realistic claim. Last time I actually experienced 11 days was with my Nokia 6310i, more than 10 yeas ago ... makes me feel nostalgic