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Amazon.com: HQRP 9V Battery Snap Connector and AC Adapter Compatible with 9-Volt/Radio/Square / 6LR61 / 7.2H5 / 6KR61 / 6HR61 / PP3 / MN1604 Clip Holder Cable Power Supply Cord [UL Listed] +
Arduino misconceptions 6: a 9V battery is a good power source