Lithium Ion Polymer Battery with Short Cable - 3.7V 350mAh : ID 4237 : $5.95 : Adafruit Industries, Unique & fun DIY electronics and kits
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Amazon.com: HXJNLDC DC 3.7V 3000mAh 103665 Rechargeable Lithium Polymer Replacement Battery for DIY 3.7-5V Electronic Product, Mobile Energy Storage Power Supply : Electronics