I always liked battery life of my l640 even after w10m update there was enough power to run through the day... I usually charge my phone every night so I don't need a 3-4 days megaphone, if you know what I mean. For me it's important that it won't die in the middle of day - and as I said before, I email a lot, do some office staff, surf the web and some phonecalls... that's what I need it for. And for me it's also important that lumia phones always sync all the emails (outcoming, incoming, etc) with my laptop, and other phones like android or iOS doesn't...