So far so good. Fully charged upon receiving and after moderate usage all day. Last night it was fully charged at midnight, so I unplugged it, and after almost 22 hours of moderate usage, it's at 77%. The past few days since I've installed it, the battery has not gone below 60%. That's usually from 5 am till 10 pm without being charged. I would really like to see these types of extended batteries for Windows Phones.