I just replaced the battery on my N5 with an OEM battery. While it's definitely an improvement, it's not as marked as others are stating on this thread. It still doesn't last the whole day, but then again, it rarely did when it was new. It was definitely worth the $15.
My GPS is somewhat flaky as well. Sometimes it just stops working and I have to power cycle the handset. Sometimes, it stops working for a few seconds.
While I love the N5, I'm ready to ditch it as soon as Bullhead is available this fall. I'd love a better battery, GPS, and camera.