Amazon.co.jp: EEMB Lithium Polymer Battery 3.7V 350mAh 702030 Lipo Rechargeable Battery Pack with JST Connector - Check the polarity of your device and connector before purchase : Electronics
Lithium Ion Polymer Battery - 3.7V 350mAh : ID 2750 : $6.95 : Adafruit Industries, Unique & fun DIY electronics and kits