Include a 9V battery pack for plug-less installation.

Can I use a 9V USB rechargeable battery (with a separate USB port for charging) with the normal 9V charger (2 poles)? - Quora

9V battery holder with switch & 5.5mm/2.1mm plug : ID 67 : $3.95 : Adafruit Industries, Unique & fun DIY electronics and kits

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DescriptionFinally, an alternative way to power your electronic devices that use a 9V battery! This 9V Battery Eliminator Kit is used to replace a

9V Battery Eliminator Kit

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Rechargeable Battery Pack for Les Paul® - shop-fishman

Portable Power Bank for Camping - Compact & Powerful

Battery Connector, 9-volt

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ESP-9V Battery Operated Irrigation Controller

Provides a handy way to connect a 9V battery to a project for portable operation.

9V Battery to DC Plug Adapter Cable

Tenergy TN295 10-Slot Li-ion 9V Battery Charger with 10 Pack 9V Li-ion Rechargeable Batteries