I also bought the 1900 anker batteries (2 pack with charger), and am very pleased with them so far
I haven't timed how long they last, but they 'feel' like they last quite a bit longer than the OEM battery. I'd say that for active users, two spares are 'a must.'
The Evo V is ridiculously power hungry (esp. compared to the wife's samsung reverb). I cycle through all 3 EVO batteries regularly, which was a shock. On my old LG Optimus, I only used the spare battery for emergencies or while on the road.
I bought my ankers from laptopmate on amazon and they were shipped crazy fast (had them in hand 3 calendar days after placing the order).