Quality replacement battery for Nokia Lumia 640 / 640 LTE. Unlike cheaper batteries found on other sites, this one is fully compatible and won't damage/ destroy your Nokiat Lumia 640 / 640 LTE. Bring your mobile phone battery back to full life! Battery Calibration: Just like when you've purchased a new mobile phone, calibrating the battery is an important step to make. For mobile phones and tablets, after you have replaced the battery, charge to 100% and leave charging for 2 hours over full charge point. Use the device until it turns off due to no power. We advise doing this is the evening after a day of use. Maybe playing a HD quality film etc. Once done, charge the device to 100% without disruption. Although doing this once is usually enough, for ultimate battery calibration, repeat the process.