Not the PiJuice specifically, but I am using the MoPi 2 (https://pi.gate.ac.uk/pages/mopi.html). This does not include a built-in battery like the PiJuice, but has two inputs that accept 6.5-24VDC, a

Some hardware stores (typically, NOT Lowes or Home Depot). In our area (PNW), Coastal Farm & Ranch carries down to M2.0. Also look for RC hobby stores. They often carry down to M1.0 for model airplane

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